Books and recordings about the variety of orchestral instruments--e.g., "Zin, Zin, Zin, a Violin," "Peter and the Wolf" (Prokofiev), "Carnival of the Animals" (Saint-Saens). The latter two musical works have the advantage that they are written in relatively short movements or sections, and have vivid imagery or a narrative attached to them, so you could take a month and use one as the spine of a thematic study.
Experimenting with making your own instruments: you can make pretty much anything into percussion (rice/pasta/bean shakers, box/tub/can drums, etc.). Rubber-band banjos can allow you to play with the effect of tension on pitch. Blow across the top of bottles filled with various amounts of water. (Or you can tap them gently, instead.)
