I agree with beignets and RobinD's advise, contact the district's attorney and get their opinion. Schedule a meeting with yourself, the attorney and the principal. Bring a list of all those businesses you are looking at approaching.
We have a local Bar/Restaurant that often buys advertisements for Booster Clubs, Adademic Clubs, etc (our PTO has never sold any for anything). When you see their ad in a school pamphlet it only advertises the restaurant, ie., lunch specials, Friday Fish Dinners, etc.- they keep mention of the tavern out of it.
I don't know what other types of businesses you are thinking of selling ads to but there are obvious "businesses" that probably should be avoided, if you know what I mean. Besides those, I don't know what other type of ad anyone could have problem with. If they have an issue about a nail salon or daycare, then they need to find a hobby (imho).
Keep in mind that, no matter what you do, you will never be able to fully please everyone and their opinions. Gather your information the best you can, follow your instinct and make your decisions. I'm sure it will turn out fine.