For years I've taken a light 8-oz 12"x16"x6" Wilderness Experience pack with me on trips as a convenient day pack capable of being rolled up and stored in carry-on luggage.  This size is just right for carrying an extra camera lens for my SLR, and adding in a light jacket, lunch, and a pocket umbrella.  I've been unsuccessful in trying to replace my 30-year-old pack until recently, when I discovered the Eagle Creek Packable Daypack.  It's an exact match in size (12"x16"x6") and has a similar 6"x7" single outer pocket for knickknacks like spare SD cards and camera batteries, lens filters, and small camera accessories.  What's better, the Eagle Creek pack only weighs 6 1/2 oz, yet it's very well made of modestly-heavy black nylon fabric with dual high-quality metal-pull Nylon-tooth zippers.  I just returned from 5 weeks in India using it every day while touring temples and museums.  I found my old pack (same size) also perfect for trekking in Nepal when the porters had our main luggage.  So, for both light day hikes and foreign day trips it's a great size...it also easily caries my 10" netbook computer if I want to take it on the plane or to a hotel-lobby hotspot.  As an added attraction, the pack has really comfortable mesh shoulder straps...a big improvement on my old pack.  Note, however, that the fabric is not waterproof...but neither was my old pack. I highly recommend it as a light travel daypack.