It's probably a good possibility that most people think about backup systems for when the juice is out. Like generators [the 1st to sell out] drawback is if outage is wide the gas stations won't have any juice to run the pumps to sell you the gas, unless they also have a generator.
Wood stoves & fireplaces also a good source, problem is you have to feed them all the time. Some fireplace inserts are pretty good at stretching the log out on burn times and wood stove construction has gotten pretty good over the years.
*Drawback is if you dump the tank over these babies don't have automatic shutoff valves and if you aren't there to catch it right away you will most likely burn your friggen house down unless you thought ahead and placed it on top of a fireproof hearth or a cement or tile floor. These suckers get "HOT"and you can get burnt real quick if you aren't on top of your game. Bottom line if you're burning one of these stay off the booze.