Unikia's Compleat Foodskin lunchbag can magically expand to accommodate more than just a piece of sandwich. And when you're done eating, it can be flat enough to slip into your bag.

The ever expanding capacity isn't the only trick up it's sleeve. It will also hold everything in place. For example, your huge sandwich has all kinds of things in it. It will look exactly the same as when you first assembled it. The lunchbox is going for $33. [Unikia]