When we did ours a couple of years back (we had about 20 people involved mind you), the main ones we did were:
First we stole the keys from the cleaner for the lock to one of the back gates, snuck in on Sunday night and...
- Put honey all over every hand rails and steps around the school
- Went to Big W, buy the rank smelling bottle of fish attractor or something like that (it was absolutely foul) and spread it over the carpets in every class room we could, as well as the principals office.
- Filled up about 500 small plastic cups with water and blue dye and carefully placed them all over the main hall in the main block of class rooms (we had block a, block b and block c, the block d's where demountable)
- Water bomb assaults from the roof top with hundreds of water bombs filled with all different colours of dye. The seniors all wore white shirts, as did year 10 students so it's safe to say we annihilated some shirts for good.
And a year before us, they flogged the Ronald McDonald statue from Maccas and glued it to the pillar out the front of the school. By far the funnies sh*t I have ever seen turning up to school that next morning.
Best days of my life. God I miss high school.