Feel free to design the film canister any way you wish. Fill the canister 1/3 to 1/2 full of water. Drop in an Alka Seltzer tablet (a half tablet works just as well too), quickly put the lid on the canister and stand the canister upside down on the ground. Do this outside!
As the tablet dissolves in the water, gas is created, filling the canister. The air pressure in the canister quickly increases and soon reaches the point that the canister blows off the top and launches into the air! Very cool! You can experiment with different amounts of water to determine how water level effects the launch. You can also experiment with the size of the Alka Seltzer tablet. You should be able to get the canisters to launch a good 15 - 20 feet in the air!