Bacon figured out how to make acetylene when we were in college. He took an old glass pop bottle (7 Up, IIRC), put a handful of calcium carbide gravel in it, added water, and started trapping the gas in balloons.
Fill a few paper bags with acetylene balloons. Take the bags to an empty dumpster (we used the one at my mother's school, since it was late summer and we knew it'd be empty). Light the bags and stand back!
It made a nice boom!