The foil thread was here. Even heavy-duty foil just isn't much good for heating water in. When you need a pot or cup, there isn't much else that will do.

Potlike containers have been extremely valuable to Mankind for several thousand years. Not having one in your kit is a serious omission, weight or bulk notwithstanding.

I always hated to see people in westerns drain the last drop of water from their canteen and then toss it. What were they planning on putting water in if they found any? Movie directors are dummies.