I need one of these.
The Gear Junkie:
It stuffs down to a size smaller than a baseball. Its manufacturer, Sea to Summit Inc. of Perth, Australia, suggests using it as a keychain. But unpack the Ultra-Sil Day Pack and its crinkly “siliconized” Cordura nylon quickly takes shape, a backpack materializing from a tiny ball right in front of your eyes.
As outdoors products go, the Ultra-Sil Day Pack is certainly strange. It is far from technical gear. The backpack, a basic sack equipped with shoulder straps, carries its stowed items with scant support. Lumps protrude from the thin fabric where a shoe or a water bottle might be stuffed inside. Objects dig into your back.
But what this $28 backpack lacks in performance it gains in improbable convenience. The Ultra-Sil Day Pack weighs just 2.4 ounces. It fits in any pocket. Unzipped and open, there’s about 20 liters of space inside–enough area to stow a day’s worth of supplies while traveling. …
besthike.com 
I’ve got one for Christmas !! (and it is a ripper!)
Beat me to the punch, got a post scheduled for next week on it!