United Airlines has changed their policy on carry-on bags - if you use the overhead it will cost you $20.  Your carry on cannot be larger than 9" thick, 10" wide, 17" tall and must fit under your seat.  I have not been able to find a wheeled bag or tote with those dimensions; however, this cute little cart DOES fit those dimensions so I can add my own small case/tote/etc and still be able to wheel it around and have it fit under the seat.