If you don’t have a generator building kit, but do have a few magnets, some wire and a long nail, you can build your own generator using the instructions on William Beaty’s website, ‘Ultra-simple Electric Generator‘. The video gives excellent, detailed instructions, but there are also written instructions with a supplies list.
UPDATE: A small group of my students tried this and, despite the complaints, I thought it was a useful exercise. I’m looking forward to their presentation tomorrow.