I'm not sure if your school is big enough, but if you can get every senior to ride the bus...that throws off the whole system. A few years ago some guys did that at my friends highschool and they didn't have enough space cause they were used to having the seniors drive.
Numbering the pigs is a good idea, some guys at my school did it. Make sure you lube em up good.
Put baby oil all over the main hall. Its a bitch to clean up.
Litter the entire halls with porno. Its best if you get a bunch of people to help you out.
You can always camp out, with the rest of you class, in the faculty parking lot. Make sure everyone parks in their usualy spots so that the teachers have no place to park.