This is a quick-and-dirty method for making a Leyden Jar (an early form of capacitor) from my old friend, the 35mm film cannister.
Step 1: Tools and materials.
35mm film cannister
Aluminium (kitchen) foil
Proper wire strippers.
Step 2: Make it.
Do the inside first - it's the most fiddly part, but once it's done you won't damage it while you do the outside.
Cut a rectangular piece of foil large enough to line the cannister. Add a few dabs of glue-stick, then slide it into place inside the cannister. Make sure it doesn't stick out of the top of the canister. Try and keep edges of foil smooth and straight, or they will "leak" charge.
Added 1st March 2007:
I've just made a load with a bunch of fumble-fingered kids, and I've worked out a method for putting the foil inside:
> Cut the foil to size, and glue the back with the stick.
> Roll it loosely around your thumb, glue side out.
> Put your foiled thumb into the pot, and gently roll the pot around your thumb several times. The foil will smooth against the inside of the pot and can be slid down into place.
Too much glue near the top of the pot is as bad as having the foil too close to the top - it turns out that it is a fairly good conductor until it is bone dry (which can be a long time inside a closed pot).