I would be surprised if the nurse was actually buying medications..... most places do not allow the school nurse to give out medicine (even OTC) UNLESS the parent has brought the medicine to school, and signed a paper for their student to take it.
However, I can see the nurse having to buy bandaids, etc...... it is amazing how much supplies the nurse goes through, kids wanting out of class, so they say they need a band-aid, etc....
I would hope that the school would have a budget for that kind of thing, though..... it is cheaper to buy those through a supplier than at a local store. Most schools allow certain items to be purchased on a purchase order through approved vendors.
Our nurse routinely gives each teacher a little "kit" with bandaids, alcohol wipes, a glove or two, etc., to cut down on those out of class excursions, and free up the clinic time for the students that really need it. (I work in a middle school.)