a preferred embodiment of the invention is shown as backpack 10 in fig1 . the sack 12 is made of a pliable material such as nylon or canvas . the sack 12 has a front wall 14 on the posterior side ( farthest from user when on users back ) of the backpack 10 , a rear wall 16 , opposite the front wall 14 , and two side walls 18 and 20 that are opposite each other and substantially perpendicular to the walls 14 and 16 . the sack 12 also has a bottom surface 22 and a top surface 24 wherein the bottom surface 22 is closer to the ground than the top surface 24 is to the ground when the backpack is worn by the user . the front wall 14 , rear wall 16 , two side walls 18 and 20 , bottom surface 22 and top surface 24 form a compartment 25 on the interior of the sack 12 . the sack 12 may be opened along the zipper 26 on the front wall 14 using zipper pulls 27 and 29 . the zipper 26 extends in an inverted u shape such that when it is completely unzipped the front wall 14 becomes a flap or door that is attached to the sack 12 like a hinge near the bottom surface 22 . the front wall 14 can be seen in an unzipped position in phantom in fig1 . two zippered compartments 28 and 30 which provide additional storage space are attached to the front wall 14 . it is also noted that additional side compartments ( not shown ) may be provided on the side walls 18 and 20 . the backpack 10 has straps 40 and 42 each having one end sewn to the top surface 24 of the sack 12 and another end sewn to rear wall 16 near the bottom surface 22 . the straps 40 and 42 could also be attached to the backpack 10 in many other ways that are well known in the art . the backpack 10 also has one or more straps 44 for attachment of camping items such as a tent or sleeping bag to the exterior of the top surface 24 . in a preferred embodiment shown in fig1 the sack 12 is supported by a frame comprising frame members 46a and 46b . the frame members 46a and 46b have a top portion in the direction of or adjacent to the top surface 24 and a bottom portion in the direction of or adjacent to the bottom surface 22 . the frame members 46a and 46b are inverted u shaped tubes . the frame members 46a and 46b can be made of any suitable material which will support the sack in an upright position , including but not limited to , steel , aluminum , fiberglass and composite materials . in a preferred embodiment , hollow aluminum poles are used for the frame members 46a and 46b . the frame member 46a includes two ends 48a and 50a at the bottom portion and a middle section 52a at the top portion of the frame 46a . the frame member 46b includes two ends at the bottom portion of which only end 48b is shown in fig1 . the second end ( not shown ) of frame member 46b is the end of frame member 46b opposite from end 48b similarly as to how end 50a is opposite from end 48a on frame member 46a . the top portion of frame member 46b comprises middle section 52b . the frame member 46a is positioned in the compartment 25 with the middle section 52a situated adjacent to the junction between the upper surface 24 and the side wall 18 . likewise the frame member 46b is positioned in the compartment 25 with the middle section 52b situated adjacent to the junction between the upper surface 24 and the side wall 20 . retaining straps 54 and 56 are used to retain the frame member 46a in the sack 12 so that the frame member 46a does not slide toward the ground when the backpack 10 is lifted off the ground . one end of the straps 54 and 56 is sewn into the sack near the junction of the upper surface 24 and the side wall 18 . the straps 54 and 56 are then wrapped underneath the middle section 52a and attached to the sack 12 via a snap or other fastening device near the junction of the upper surface 24 and the side wall 18 . velcro ® hook and loop fastening material could also be used to removably attach the retaining straps to the sack . likewise , the frame member 46b is retained in the sack 12 by retaining straps 58 and 60 . the ends 48a , 48b , 50a and second end of frame member 46b ( not shown ) generally extend at least to the bottom surface 22 of the sack 12 . in this way , the ends act as legs upon which the backpack 10 can stand upright . in a preferred embodiment shown in fig1 the ends 48a , 48b , 50a and second end of frame member 46b ( not shown ), extend through holes in the bottom surface 22 of the sack 12 . the ends 48a , 48b , 50a and second end of frame member 46b ( not shown ) are therefore an extended base upon which the backpack can stand . the extended base formed by ends 48a , 48b , 50a and second end of frame member 46b ( not shown ) keeps the bottom surface 22 clean and dry by keeping it off the ground . if desired , rubber cups ( not shown ) may be placed on each of the ends 48a , 48b , 50a and the second end of frame member 46b ( not shown ) to protect the user from a sharp edge of the ends . fig1 shows two removable and moveable shelves 62 and 64 which divide the compartment 25 into three subcompartments . the shelves are attached to the sack 12 with a fastening material such as a velcro ® hook and loop fastener or by any other type of releasable fastener such as a snap that releasably connects the shelf to the sack 12 . one or more such shelves may be used . a preferred shelf 64 is shown in fig2 . the shelf 64 includes a stiff portion 66 made of plastic encased in nylon . alternative materials may also be used for the stiff portion , for example cardboard encased in canvas , plastic encased in canvas or cardboard encased in nylon . opposite ends of the stiff portion 66 include first and second flexible flaps 68 and 70 respectively . the flexible flaps 68 and 70 are extensions of the nylon from the stiff portion 66 but without extension of the stiff material , namely the plastic . the plastic ends at the joints 72 and 74 between the stiff portion 66 and the first and second flexible flaps 68 and 70 . therefore , the flexible flaps 68 and 70 are hinged at the joints 72 and 74 . in a preferred embodiment hook and loop fasteners 76 and 78 , such as a velcro ® hook and loop fastener , are sewn onto the outer surfaces 80 and 82 of the flexible flaps 68 and 70 respectively . the hook and loop fasteners 76 and 78 may also completely cover the flexible flaps 68 and 70 if additional fastening strength is needed . the side of the side walls 18 and 20 facing the compartment 25 are covered with a hook and loop fastener such as velcro ® hook and loop fastener that will mate with the hook and loop fastener strips 78 and 80 . the hook and loop fastener on the side wall 20 can be seen in fig1 as reference numeral 84 . the hook and loop fastener on the side wall 18 is reference numeral 86 . the hook and loop fasteners 84 and 86 on the side walls 18 and 20 extend substantially from the bottom surface 22 to the top surface 24 and substantially from across the width of the side walls 18 and 20 from front wall 14 to rear wall 16 . the hook and loop fasteners 84 and 86 are either sewn or glued to the side walls 18 and 20 respectively . velcro ® hook and loop fasteners are sold with an adhesive backing . the shelf 64 is attached to the sack 12 as shown in fig1 by mating the hook and loop fastener 78 ( shown in fig2 ) to the desired position on the hook and loop fastener 84 on the compartment side of the side wall 20 . this desired position can be anywhere along the length of the side walls from the bottom surface 22 to the top surface 24 . likewise , hook and loop fastener 76 is attached to the compartment side of the first side wall 18 by mating it with the hook and loop fastener 86 . in its utilized position , the shelf , including the flexible flaps 68 and 70 and the stiff portion 66 form a u shape with substantially square corners . the shelf 64 may be removed from the sack 12 by pulling the hook and loop fasteners 78 and 80 of the shelf 64 away from the hook and loop fasteners 84 and 86 respectively . the shelf 64 can then be reattached to the sack 12 at a different location or it can be removed from the sack 12 resulting in a larger subcompartment or use of the entire compartment 25 if desired . in this way any number of shelves in any position can be utilized to make this a very versatile backpack . in a preferred embodiment a webbing 90 is connected across the front edge of the shelf 64 to prevent items on the shelf from falling out of sack 12 when the front wall 14 is opened . the front edge of the shelf 64 is the portion of the shelf nearest the front wall 14 . the webbing is made of a rot resistant synthetic fabric such as nylon . the webbing is attached to the shelf 64 by sewing it to the front edge ( edge nearest front wall 14 ) of the flexible flaps 68 and 70 and stiff shelf portion 66 . the features of shelf 64 discussed throughout this application are also utilized in the other shelves such as shelf 62 shown in fig1 . many such shelves may be utilized . the backpack 10 can be easily stored without taking up much space by compressing the backpack 10 . the backpack 10 can be compressed by removing the shelves 62 and 64 and any other shelves from attachment to the side walls 18 and 20 , and moving the u shaped frame members 46a and 46b towards each other while at the same time compressing the sack 12 . it is noted that this invention also contemplates use of frame members situated across the front and rear walls 14 and 16 as opposed to across front and rear walls as shown in fig1 . in such an embodiment the frame members would be perpendicular to the positions of the frame members in fig1 . the backpack 100 shown in fig3 is an alternate embodiment of the invention . the backpack 100 includes a sack 102 and a frame comprising two u - shaped frame members 104a and 104b which include retaining brackets 106 and 108 respectively . the retaining brackets may be attached to the u - shaped frame members 104a and 104b in any manner known in the art including , but not limited to , by weld or bolt . the backpack includes a first sleeve comprised of the rear wall 110 and the outer rear wall 112 which are both on the anterior side of the backpack 100 . the outer rear wall is a substantially rectangular sheet of material ( e . g . nylon ) that is sewn around its perimeter to the perimeter of the rear wall 110 . an opening is left between the outer rear wall 112 and the rear wall 110 at the bottom of the rear wall 110 and outer rear wall 112 near the bottom surface 114 of the sack 102 . the frame member 104a slides into the first sleeve in the backpack such that the middle section 116 of the frame member 104a is situated adjacent the top surface 118 of the sack 102 . in fig3 the frame member 104a is shown inserted about halfway into the first sleeve . in order to prevent the frame member 104a from sliding out of the sleeve when the backpack 100 is lifted from the ground , one or more retaining straps may be used . one side of the retaining strap 120 is sewn to the outer rear wall 112 . when the frame member 104a is fully received by the first sleeve , the retaining strap 120 is wrapped underneath the retaining bar 108 and the end of the retaining strap 120 opposite the sewn end is removably attached to the bottom surface 114 of the sack 102 . the removable attachment of the retaining strap 120 to the bottom surface 114 can be performed with any means including but not limited to velcro ® hook and loop fastening material 121 or mechanical snaps . the retaining strap 120 can be unhooked from the bottom surface 114 to allow removal of the frame member 104a from the first sleeve of the backpack 100 . note that retaining strap 120 is shown in fig3 in a position detached from the bottom surface 114 . other ways of holding the frame member 104a into the first sleeve may be employed such as a retaining strap within the sleeve near the top surface 118 that wraps underneath the middle section 116 of the frame member 104a . an opening in the rear wall 110 or outer rear wall 112 near the top surface 114 would be needed to have access to such a retaining strap and the middle section 112 within the sleeve . if this form of retaining the frame members in the sleeve is employed , then the retaining bracket 108 and the retaining strap 120 are not necessary . the frame member 104b is situated in a second sleeve parallel and adjacent to the front wall 122 which is on the posterior side of the backpack 100 . the second sleeve is comprised of the front wall 122 and the outer front wall 124 which is adjacent and parallel to the front wall 122 . the outer front wall 124 is similar to the outer rear wall 112 and is sewn to the front wall 122 on three sides just as for the first sleeve . the fourth side of the outer front wall 124 along the bottom surface 114 is not sewn to the front wall 122 thereby providing an opening within which the frame member 104b can be received . any additional compartments or pockets 126 and 128 that would be on the front wall would be attached to the outer front wall 124 as shown in fig3 . a retaining strap 130 is shown in its attached position in which it is wrapped underneath the retaining bracket 106 and attached to the bottom surface 114 of the sack 102 . it should be appreciated that the embodiment shown in fig3 is not meant to limit this invention to the use of frame members located along the rear wall 110 and front wall 122 of the sack 100 . this invention certainly contemplates the positioning of sleeves along the side walls of the sack along with insertion of frame members into those side wall sleeves . an alternate frame 200 is shown in fig4 . the frame 200 includes a top portion 201 , a vertical portion 203 and a bottom portion 212 . the frame may also include a bar 202 which provides structural support to the frame 200 . the frame 200 may be separated into two parts along the junction 205 near the top surface . the top portion 201 mates with the vertical portion 203 at the junction 205 by slidably receiving vertical portion 203 or by slidably being received by vertical portion 203 . fig5 shows a backpack 204 of the invention , including frame 200 . the frame 200 supports the sack 206 . fig5 is a side view of the backpack 204 with the top portion 201 of the frame 200 received in a sleeve 208 which is positioned adjacent the top surface 210 of the sack 206 . the vertical portion 203 of the frame 200 is positioned outside the sack 206 but adjacent to the rear wall 222 of the sack 206 . the bottom portion 212 of the frame 200 is in the shape of an inverted v to prevent the bottom surface 214 of the sack 206 from contacting the ground but still allowing the backpack 204 to stand upright . shelves 216 , 218 and 220 are constructed and attached to the backpack the same as discussed above for the other embodiments . the vertical frame portion 203 is held adjacent to the rear wall 222 by two or more retaining straps 224 and 226 which wrap around the vertical frame portion 203 . one end of retaining straps 224 and 226 is sewn to the rear wall 222 of the sack 206 . the other end of retaining straps 224 and 226 is removably fastened to the rear wall 222 with hook and loop fastening material , with mechanical snaps or other means . the middle portion of the retaining straps 224 and 226 is wrapped around the vertical portion 203 of the frame 200 . backpack 204 is assembled by sliding the top portion 201 into the sleeve 208 . then vertical portion 203 is mated with top portion 201 bringing the remainder of the frame into place adjacent to the rear wall and bottom surface of the sack 206 . straps 224 and 226 are wrapped around the vertical section 203 and snapped or otherwise fastened to the sack . the foregoing description of the preferred embodiment of the invention has been presented for the purposes of illustration and description . it is not intended to be exhaustive or to limit the invention to the precise form disclosed . many modifications and variations are possible in light of the above teaching . it is intended that the scope of the invention be limited not by this detailed description , but rather by the claims appended hereto .
a backpack including a sack and a frame , the frame extending at least to the bottom surface of the sack such that the backpack can stand upright . the sack encloses a compartment which can be divided into subcompartments by shelves which are movable and removable for accommodating items of various size and shape . the frame holds the sack upright for effective use of the shelves .