You can build a drum kit pretty easily if you have Arduino, Bluetooth and a Smartphone. Here we have made a DIY Bluetooth drum kit that takes input from a Piezo and plays it from your phone.
The whole thing fits into a box and sound is played from your phone via Bluetooth. This make the everything portable
We did this as part of our kickstarter called Jetpack a wireless programing Bluetooth shield and motor driver shield for Arduino. You can use your own substitutes for this.