I've never really worked two jobs at a time, but if I were to pick a second job that I'd do for enjoyment, it'd be working in a convenience store. I did that all through high school and a lot in college, and I really enjoyed it. Lots of interesting things happen, and at a small store the staff is like a family. Unfortunately the pay is not so great.
Another job I really liked was custom closet installation (like California Closets). It kept me in good shape (going up and down stairs all day, carrying heavy materials), and it presented a lot of challenging problem solving situations. It paid a lot better than the convenience store, but I think the guy I worked for paid better than average for that job (he only lasted a few years; really he only lasted for one year, but he didn't want to let it die).