of course it´s possible to bring water in a paper container to a boil - no doubt about that. Im not sure about freezer bag cooking, at higher temperatures some of the bag´s material might "go" into the food.
And of course it´s all about bushcraft here, no doubt our ancestors used birch bark, wood, clay, animal skin and whatever they had - probably no titanium, not sure about those folding plastic stuff
whith my critics I just wanted to make a point about some downsides of folding flat cookware and for sure not to put them down in total.
My apologies if this wasn´t clear.
Best on this discussion is to learn from others - thanks a lot for the ideas.
For sure I´m now prepared for the worst case: beeing somewhere in the wild and having no Trangia and no titanium pot with me all I´ve to do is to find birch bark