Make a one-string "guitar" by stringing a cup with some fishing line. You amplify the plucking of the string by placing a piezo contact microphone and mini battery powered amplifier inside the cup. Piezo contact microphones amplify physical vibration, unlike regular mics which pick up sound waves from the air. Stretching and plucking the string produces different notes. Attaching the string to different items can amplify the tapping on a wooden table, or the scratching on a piece of cardboard!