Step 1: You will need......
A matchbox ! (standard matchboxes are usually just the right width for 35mm film)
A new roll of 35mm film. Any type will do, but normal colour print film 100 or 200 speed works very well
An empty roll of 35mm film with at least 1cm stub of film sticking out. Ask at your local photo labs, they normally throw away/recycle these.
Some thin cardboard (the box the new film comes in is fine)
An empty aluminium drinks can
Black PVC electricians tape
The plastic from a spiral binder, or any small piece of thin, curved plastic
A fine sewing needle or pin
A sharp craft knife
A black marker pen