When doing festivals, I keep about 3-4 gas cans in the truck bed so I can power my generator. I still keep a few cans full just in case, and this thinking helped when Austin had its fuel "crisis", since all I needed to do was empty the fuel cans and generator tank for the week when all pumps were either shut down, or had people physically brawling at the pumps.
When I was renting a "B", I found that having a hitch mounted cargo carrier, a CarPod rack with high walls and a locking top, and several five gallon gas cans secured inside made a drive a lot easier, because I could just use a gas can if I couldn't find a usable gas station.