I like to fiddle with things, any suggestions?

I've bitten my nails for most of my life, I'm 17 now and they arn't very nice. I've managed to prevent myself biting them with reasonable success, however if I'm on my laptop I often end up biting them without realising.

I enjoy fiddling with things, I keep a zippo in the pocket of my overcoat and I open and close it in my hand. Do you know of any cheap (doesn't have to be dirt cheap) toys, gadgets, things that I can fiddle with? I'm tempted to get a gyroscope but it takes time to wind up.

P.S.

I don't care if I look immature cos I'm playing with a toy :P