My school made Year 12 a really enjoyable year. Lots of events planned throughout the school calendar as always, but there were some events that were directed primarily at senior school students, i.e
Senior Social in May
Year 12 Formal at the Grand Hyatt in September
Year 12 MHS vs Mac.Rob cup (throughout the year)
Year 12 Interform Futsal competition (first-second terms I think)
Valedictory Night (although many of us missed it because we were on Schoolies)
Those are just a few from the top of my head, but final-week activities were the best for me. We went bowling with teachers, lit our hands on fire (literally - using methane bubbles), and all sort of whacked crap like drinking dyed milk and vomiting it all over the front of the school (which is really just a Year 12 tradition)
There's also the Year 12 jumper which we got in Term 4.
Unfortunately we didn't get a common room though, oh well