I graduated from high school just a few years before Crowe. I don’t remember anyone ever ordering food for delivery to a classroom. And if you had asked me, I would have assumed it would have been against the rules. But there were no physical barriers to doing it, assuming you could get the delivery person to comply.
I thought the whole point of Spicoli doing it was to show how little regard he had for rules, setting him toe-to-toe with the no-nonsense Mr. Hand. And to hint at his weed use, via the constant munchies.