Rocket+Film+Canister

What you will need: One empty 35mm plastic film canister and lid (visit any store that has film developing and they will usually give you some of these for free. The white canisters work much better than the black ones do.) One fizzing antacid tablet (such as Alka-Seltzer - Get this from your parents) Water Safety goggles What to do: //Do the next 2 steps quickly//
 * 1.** Put on those safety goggles and head outside. No really, when this works, that film canister really flies! If you want to try the indoor version, do NOT turn the canister upside down in step 5.
 * 2.** Break the antacid tablet in half.
 * 3.** Remove the lid from the film canister and put a teaspoon (5 ml) of water into the canister.

Caution: If it does not launch, wait at least 30 second before examining the canister. Usually the cap is not on tight enough and the build of of gas leaked out.
 * 4.** Drop the tablet half into the canister and snap the cap onto the canister (make sure that it snaps on tightly.)
 * 5.** Quickly put the canister on the ground CAP SIDE DOWN and STEP BACK at least 2 meters.
 * 6.** About 10 seconds later, you will hear a POP! and the film canister will launch into the air!

Source:http://www.sciencebob.com