Six empty beer cans (the old ones you used a pointy opener to get to -- before pull tabs), matches, a ten penny nail, can opener, lighter fluid, some aluminum foil and Duct tape.
Take out both ends of 5 of the cans and tape them end to end. The sixth can got two more openings for a total of four. Then you turned it over and punctured it with the nail. Tape the end with the 4 holes to the end of the other five . . . leaving the loading/firing hole exposed.
Squirt just a couple of drops of lighter fluid in, hold the unit with the open ends down and shake back and forth two - four times.
Point in a safe direction, light a match and put it against the loading/firing hole.
Sounds like a military cannon.
DO NOT ATTEMPT WITH ANY PULL TAB CANS! They are aluminium and will not stand up to the pressure and could injure the user.
For added fun, wad up a bit of aluminum foil nice and tight to a size 1/2" smaller than the diameter of the barrel. Will fly (if done properly) 70 - 100 yards. Scares the heck out of the neighbors as well.