You know those little bang snaps you throw at the ground and they make a popping sound? For DIY, ideally, I'd do things in that kind of volume. I'd probably need a smidgen more, but I wouldn't want to do more than e.g. make a pinhole in 29 gauge sheet metal.
What I'd really love to make -- but I don't think I ever could safely -- is a little 1/8A or 1/4A rocket engine (of the that cost a couple bucks at the local hobby store).
This is science lab with kids, not bomb-making 101.