I second the mention of a guitar (or some sort of musical instrument) if you're not already into that. You can spend a lot of time on it and it's something you can really fall in love with.
If you've ever been interested in computer programming / web development, graphic design, or anything like that it's a perfect time for that, too. There are loads of training materials online that you can follow along with and learn all sorts of geek skills that can make you some good money.
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