I loved Halloween celebrations as a kid! The first part of the school day was actually school, but right before recess, we would have a big assembly. Everyone would walk across the stage in their costume (because everyone would come to school dressed up as something lol) and then they would have a costume contest for each grade.
Then after the winners were announced, everyone would go back to their homeroom and gouge themselves on junk food people brought (cupcakes, sandwiches, finger food,etc.). I don't remember any food being crappy, but hey - this was the south so you know it was probably good.lol
Then there was recess and we would leave to go home early. I don't know if they still do that (I doubt it) but I LIVED for that day. In second grade, I won the contest when I came to school dressed as Snow White.
I think I still have that trophy somewhere.lol