How will people in the more heavily populated areas get fuel for cooking?
Propane, kerosene, White gasoline.
Something else that points out the importance of planning of whether to evacuate or not.
Deconstruct your tinfoil hat and tape it to a carboard box. Viola! You just made a solar oven that uses free fuel from the sun.
Actually, in a crisis scenario where there is an extended break in infrastructure and/or utility services, by the time the event happens the time for getting fuel or anything else will be, for all practical purposes, gone. That's why it's so important to ask those questions to oneself now so that you can assess what you would need to do now pre-SHTF to prepare and ensure you were able to continue having sources of fuel to cook food.
In that line of thought, you have several options, i.e. buy a coleman stove and several gallons of Coleman fuel like one uses when camping, or buy a single or dual propane burner, or better yet, a propane BBQ grill and keep several 20 lb. tanks of propane on hand. There are other options as well. It just depends on the option that works best for that individual.