I remember taking a used CO2 cartridge from a pellet gun, boring the puncture to as big as possible and filling it with ground-up powder from an M-80. Then you stick the M-80 fuse in the CO2 cartridge and epoxy it in. When the epoxy was set the next day, you could use it to basically blow up a tree.
In Cub Scouts, we carved rockets out of wood, inserted a CO2 cartridge into the back end, and then had them whiz across the school auditorium along a clothesline-like wire. There was even a spring-loaded tool with a needle that we used to set them off by puncturing the seal on the cartridge. These could be bought at hobby stores.
I had a plastic model car that was designed to have a CO2 cartridge inserted into the back end. The car was constrained on a tether and when the cartridge was fired (with the aforementioned tool), it would whiz around in a circle. It went around so fast it was barely visible.