Part of the criteria for my project was that my 'Grenade' had to be transportable, rather than the more traditional rockets which started the reaction by being inverted. I wanted mine to be able to be inverted, and even lightly shaken (not too hard though).
It is important to note that the person weilding a chainsaw-bayonet in my profile picture is not me!
Step 1: Step one - acquiring the materials
Some vinegar (enough to half fill 1 canister, but more if you intend to repeat)
Some baking Soda, ie bicarbonate of soda (again, enough to half fill 1 canister)
Some ordinary kitchen aluminium foil - about 2 square inches per grenade
Some tape - you will need something strong enough to make a decent seal, I used something resembling insulation tape from my dad's workshop
Something heavy and uneven - I used a steel nut
A pair of standard film canisters - I got mine from a photography centre down the road