Coffee can and a soup can,fill coffee can with about 2" of water,cut the end off the soup can and poke a hole in the center of the other end of soup can,stick black cat or zebra in small hole in soup can about 3/4 of the way in,set open end of soup can in coffee can with water, light fuse and watch that soup can go about 25 to 50+ feet into the air...we could spend hours doing this and for some strange reason it was funnier then heck.
Cant forget pop bottle rocket wars either another fun time passing thing to do until someone gets smacked. Yep 60's and 70's were fun if you can remember most of it hahaha.