If a band parent is particularly good with a sewing machine, a few stitches and seams on a blanket can transform it into a form fitting instrument cover. Don't throw away those replacement timpani head boxes. If you don't have head protectors or drop covers for your drums, make circular discs out of those cardboard boxes. Cloth or felt glued on Masonite is also an inexpensive way to make drum covers. By labeling the discs with the drum sizes your percussionists will learn how to identify the drums correctly.
Percussionists are musicians like everyone else in the band.
Other instrumentalists have to purchase or rent their instruments. Sticks and mallets owned by the school need to be stored in cases or cabinets, not left on the instruments where others can get to them. The band director's office is a good place to keep mallets such as bass drum or tam tam beaters and chime mallets if storage in the band room is not available. The extra effort in collecting mallets after rehearsal will result in much less stress and confusion at festival and concert time. Plastic sandwich bags and rubber bands make great timpani mallet felt protectors.