Having a way to cook if the SHTF is obviously a given, having a way to cook with less fuel is the smartest thing to have. A rocket stove can boil water and cook food on only a few sticks and twigs. They are super efficient.
You can buy them for around 100 bucks, but why spend that money when you can make your own for a fraction of that cost. See how to build a large rocket stove below