Oh god, I never really thought of it as a stimming thing. I thought I might have dermatillomania, considering I have always had an obsession with picking and biting at my skin if there are any ridges, bumps, or anything other than smooth. It's probably just the autism though. As far as things to do in school for stimming, I've started sketching. I let all my instructors know exactly why I sketch during lectures, and it has been the very best way for me to keep my hands busy and avoid eye-contact while still paying attention, and not being a nuisance.
I am a Graphic Design major, but I would still suggest sketching, even if you aren't drawing anything resembling... anything. It keeps the hands busy, and if it happens to improve your drawing skills over time, I'd say that is just another perk. I would suggest a pen/pencil and a small sketchbook. Doesn't really need to be more than a 3.5x5inch booklet.