This is hardly a new idea, but I wanted to show it. If you need a spare quart of gas to get you or your buddy to the next gas station. Get an MSR camp fuel bottle from the camping store, about $20.
Get a roll bar fire extinguisher holder from the 4x4 store, about $20.
Strap it all to the frame tube and you're got to go. Gas pump nozzle fits fine. I recommend left side mount away from the hot pipes in case the cap comes off, but the cap shouldn't come off if you put it on correctly.