You may be without electricity or natural gas for a number of weeks or months, and it important to have both fuel to cook with, and a camp stove to cook on, that burns a specific fuel type.
Propane is the most common fuel source to keep around (store it in your garage, in a shed, or outside under a tarp -- don't store it in your home, as it can have a slow leak and poison the air).
To conserve propane, turn to a smaller propane camp stove during a time of disaster, rather than use your barbecue. That outdoor barbecue will likely use quite a bit more propane than a smaller propane camp stove. Propane camp stoves are designed to work with much smaller bottles of propane than your standard barbecue.
To connect a camp stove to a much larger propane tank, you need a special fitting:
With this fitting you can now connect your camp stove (which uses a lot less fuel) to your barbecue size or larger propane tank.
With just a few small sticks, paper, brush, etc. you can get a small fire burning within seconds, and quickly cook food in a small pot or pan within a few minutes. It's small enough to carry in a backpack and popular with a large number of backpackers, hunters, and people who fish.