Kind of on the heels of the (no) dining hall trays  idea:
I just saw an item in the Sunday paper about how Ireland has instituted a 33 cent tax on disposable shopping bags. The government accompanied the tax measure with a public education campaign about the evils of non-biodegradable plastics. Minimal push-back. 92% market penetration. People now, it says, keep reusable shopping bags in their houses, in their cars, even at work. And to carry a disposable shopping bag in public is to invite contempt. Merchants even like it, because it reduces operating costs and storage space requirements.
For campuses, this sort of a step will probably be mostly symbolic. Students don’t make very many retail purchases on campus, and usually carry some sort of backpack/bookbag anyways. But symbolism can be important. Eliminate (or charge for) plastic shopping bags at your bookstore. Do it now. (Unless you want to wait until the campus newspaper makes a stink about it!?)