I'd probably put some photos, my favorite books and dvd's. Right now I can't think of much I'd like to conserve for 50 years (apart from myself. xD), so...

Well, the last pages of my notebooks are all filled with doodles or random words or any other thing that just comes to my mind.
When the person that's sitting next to me is trying to keep herself from falling asleep as well, I'll just get a paper and we'll talk about something, writing to each other as the boring class keeps on being boring.