Fun thing to do in the days after Halloween, when the giant bags of candy are 50% off: wander around your school or your workplace or wherever you're hanging out, go up to people at random and go "Reverse Trick or Treat!" and hand them a candy bar. I've found that people get *really* excited to be randomly given a candy bar. (Especially people who don't normally get noticed, like the dorm's housekeeping staff, and the school librarians.)
It's a fun post-Halloween thing that I'd love to see spread around.