I looked at that site, and they do have some nice metal containers - but like wow man! they have these plastic spare battery carriers that are just totally awesone!  how stupid I've been all these years to just put a couple of spare batteries in a sandwich baggie and wrap with a rubberband.

alternatives to boiling waterin a "tin" could include making a birchbark pot, and heating some small stones in a fire and dropping into a ziplock bag of water, or into a "container" made from that piece of aluminum foil, which is what I'd be doing more or less