Oxygen I'd try to avoid, personally. The tank is only $70, but the darn regulator probably runs $100+. Technically there are laws about securing it during transport. It's too heavy to carry for long distances. I work at a stadium sometimes, and we've only just gotten O2 to our foot teams this year; they're the C size, and have enough air for maybe 15 minutes. The D tanks probably could run from 20-60 minutes depending on the flow rate. OK, if you're car camping, but forget it for a backpack trip. Lastly, you need a physician to order O2, which shouldn't be a problem.

Something probably better would be a compressor, like you see the old folks that smoke-like-a-chimney carrying at the mall. Pricier too though.