Painting parties. They're definitely more fun than should be legal. My robotics team got almost as much paint on ourselves as on the walls of our build site.
Formal dinner parties. Especially how amazing it is that only 48 hours after our paint-covered adventures, my team was able to all appear formally dressed (on a school night, no less!) to host a dinner party for all our mentors to thank them for all their hard work and help.
Car rides at night just after it's rained with the windows down and your hair blowing around. The fact that the person giving me a ride home was someone whose company I quite enjoy didn't hurt either.
Perhaps I should just save a lot of time and assign my whole robotics team and everything having to do with it to the Shire.
I also assign prom. Sure, everyone says it's overrated, but I had a lot of fun, even without a date. The only bad thing was the weather (35-40 degrees F and raining) and the great discomfort caused by my high heels.