With a little software and some stuff you have around the house, you can make a simple drum trigger. A fancier version would use a real drum pad, a piezo transducer, and a cord with a headphone-jack; but this can literally cost you nothing to play around with.
Using a free VST app you can use the mic in to control MIDI events. It can be used to control drum machines or simply trigger samples.
Step 1: Equipment and Tools
What you need:
set of old headphones (only one side needs to work)
empty soda can
cassette tape case (or whatever case you like)