To relate to prepping, I think soups are going to be one of our main stays when times get bad. First they are pretty inexpensive to make. Second you can make them easily over an outdoor fire. Even if you don’t have a big witch’s cauldron .. Third you can make a lot, a minimum of labor for several days of eating.
I never did much with a homemade cardboard and foil solar oven but it certainly does have potential. Cooked rice in it and it had a wonderful nutty flavor. Of course heating veggies and soups would be easy. No smoke so no one need know you’re there or with food.