I remember back in high school economics we learned about the stock market. We all had fake money and chose companies to invest in. Then we watched as our funds raised or plummeted. It was all really exciting and since it was fake money it didn't really matter if you lost, it was just fun.
Do you do anything with stocks? I have! If you have the extra money sitting around it could be a good investment. Of course, you want to know what you are doing first...
I found this stock game online called Wall Street Survivor where you use fake cash and you "invest" in real companies with the real stock market conditions. It reminds me of how we learned to do it in high school! It's free, so if you are interested at all just visit the website and check it out! It could help educate you on the stock market and help you earn some extra money!
Have fun :).