Some simple musical instruments you can make yourself are finger bells composed of washers and dowels and a mbira composed of scrap metal and screws. Make a flute just by drilling holes into PVC pipe.
To make a maraca, all you need is tape, two paper or plastic plates, and dry rice or beans. Put the dry food onto one of the plates, then put the second plate face-down on top of it, and seal the two together with the tape. Another simple instrument is the pot bell, which is a terracotta pot with a knotted rope pulled through a hole in the bottom. To make a mallet to play the bell, use a stick covered in something like soft filling and tape.