~ Flip over an empty garbage can and hit it with a stick. Ta da! You have a drum.
~ Stretch come rubber bands over an empty Kleenex box. Ta da! You have a guitar.
~ Line up 6 glasses and fill each with a different amount of water. Tap with a pencil.
Ta da! You have a 'glass harp'. (Add food colouring for fun!)
Here are some more ideas for creating instruments out of objects you may have at home.