An equalizer T-Shirt (obviously). Mine came from here: http://www.thinkgeek.com/tshirts-apparel/interactive/8a5b/?cpg=ab
A 2-way switch (must have six connections on its underside)
A mono headphone socket
A bit of wire (I only used about 20cm/8in, but get a metre or a yard so you have plenty of spare)
Small phillips head screwdriver
Hot glue gun (or super-glue, or anything good for plastic).