If you don't want to be in stocks, bonds or mutual funds, then keep it simple and stick to what you know.  I for one know a fair bit about numismatic coins. I know a guy, all he does is spend his money on vintage electric guitars and he has done quite well.
Some people like real estate.  The point is, stay in your comfort zone, talk to people and only invest when you can get in cheap.  You can't really go wrong.