The optimal shape of the boiler - an oval with a flat bottom. The best material - titanium, but it will fit, and aluminum, and steel. In the mushroom field, or where you can catch fish, not more than would be the pan, as an alternative to cooking pan.
The mountains do not prevent an autoclave - a marching version of a pressure cooker, or on the cooking will take too much time. However, even this has benefits, nutritionists say that food cooked over low heat, keeps the nutrients, taste better and are well absorbed.