There is a lot of things that goes into a game and one important thing is sound and music.
I have played around with Garage Band which is included for free if you have a Mac. For 38 SEK you get all instruments you need. (At least for an amateur like me.)
Anyway, it is a lot of fun and a superb tool to use!
Here are a couple of tracks that I produced after a couple of hours with the tool.