I built a color organ from a kit and housed it in an altoids tin. Using a phone clip and velcro strap I made it wearable so it can be worn to the club. A color organ is a circuit that flashes a light when it hears sound.
Here's a peek inside:
Video in action!:
I also thought about making it into a belt buckle, or have a shirt with a pocket in the chest to slip this into...