Principal for a day ..eh? Well one of the things i would do is the thing you want to do...
I would give everyone a day off for 1 day so i have to do nothing, and they can have fun.
but i would like to ... this is actually reaaaallly hard! But i would probably put all the really bad behaving pupils in a classroom with the strictest teacher there is! This is probably because in my school there are quite a few people who are like a HANDFULL might i say!