I have gone a slightly different route over solid containers. I use the art of origami and thin aluminum to make a pot that is 6 inches square and 3 inches deep yet will fit into a wallet.

While you could start with heavy duty aluminum foil I decided to go a bit heavier for something that would last longer. This is to use disposable aluminum cookie pans or sometimes labeled as oven liners. These are essentially double or maybe triple the thickness of the foil. This heavier foil also results in a sturdier pan. But you still need to manuver it caregully to prevent it from unfolding when full.

I cut out a square 12 inches on a side. Using paterns of origami that can be found all over the web you can fold this into the aforementioned box that is liquid tight and reasonably ridged. Folded flat it produces a 6 X 6 inch package. Then if folded in half this gives a 6 X 3 inch packet less than a 1/4 inch thick. This packet is about the size of several stacked dollar bills. Hence will easily slip into the bill compartment of any wallet.

Yes wear and tear will eventually wear holes and need replacement. But it is very cheap, light weight and compact.