Make a compressed air rocket.  Thanks to Make Magazine, here is a step by step guide to making a compressed air rocket.  From here you can progress to the real stuff! Make Magazine shows you how to make all sorts of useful stuff cheaply at home.  A great magazine if DIY is your hobby.

A hobby such as this can also be related to on line casino which is an entertaining pastime but there are risks involved. You will succeed if you have an edge. The skill of creating something out of cheap stuff you find at home is the skill you need in finding a bet that your fellow bettor is unaware of.