I can think of a few ideas. You put your suvival kit in the plastic container and include an empty spam can with almost no wasted space.

I tested it on a gas stove rather than a wood fire, but I was able to boil water in a spam can without burning off the white coating on the inside.

I've also seen half height cans of spam in one store, so you could use two of those, or even one empty and one with spam still in it and have room left over for survival gear.

I think at one point they also sold cans that came with a plastic cover. Wish I had saved some.