You know that thing you spend your free time doing for free? Well, it might just be able to earn you a buck.
Ok, so I doubt proofreading is something you do to unwind on the weekends, but, hey, I could be wrong. It's much more likely that you're blogging, though. Put a little elbow grease into that and you could get a little cheese out of it.
I'm not into baking, but I am into eating baked goods. Since I share this trait with the vast majority of humanity, there will always be a market for delicious cookies, brownies, blondies, and all other -ies you can think of.
If you can draw, there aren't enough good webcomics in the world, either. Sexy ones are particularly lucrative, and there's a market for any genre you please. There's a lot of expensive equipment, such as drawing tablets, you might want to invest in, but if you're good at drawing and have an entertaining story idea, just draw on it a piece of paper and upload a good picture.
Your hobbies can make you money, but are they improving your mind? Check out our 5 Hobbies That Can Make You Smarter infographic, you might be boosting your brain without realizing it.