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.
I remember those!
Awesome memory.
God bless CARBON!!!
Another fun thing was to take the old metal tennis ball cans, put one tennis ball in, pour some gasoline over it and throw in a match. The pressure would build up and shoot a burning tennis ball about fifty feet.
I also remember taking three foot sections of pipe and using it as a launcher for bottle rockets and having wars with them.