Kiva Keychain Backpack

The Kiva keychain backpack is a small keychain that expands to the size of a full backpack in case you have an emergency where you need to carry things with no prior notice. For me it comes in really handy when I need to go to the local market, I can walk in with no backpack on my shoulders, and leave with a backpack full of great things that I never paid for.

Alternate purchase link - Different bag but works the same way...