2) Earth blows up or otherwise becomes uninhabitable; we float around in space looking for a new homeworld
3) The polar icecaps melt and we live on rafts, like in the movie Waterworld.
Kudzu Bob posted that I had forgotten one of the most important scenarios: 4) Zombie apocalypse.
He's right. I haven't included the zombie scenario because I'm not prepared for it. I've been spending all my time on the raft and the armored dune buggy, and I just don't have enough time left over for the shotguns or the chainsaws, etc. That planning would entail. I promise I will work to rectify this as soon as I'm able. Money is tight since I lost my job as a chicken sexer, and my wife is constantly on to me to quit messing around with flamethrower plans, so I have to keep my head down. Thank goodness she doesn't know about my blog.