Read a book, graphic novel, whatever form of literature you're in to.
Play games (the non-computer/console kind) - puzzles, board games, Sudoku, cards, volleyball, basketball, tennis, etc.
Write (not a paper) - journal/diary about your college experiences, letter to a friend, letter of appreciation to a soldier serving overseas, etc.
Share your hobby, find someone who hasn't had the opportunity or time to learn a new hobby-we can all benefit from each other's expertise.
Cook meals instead of getting take-out, save some money and refrigerate the leftovers or entertain friends/guests with a dinner. (we all have to eat, right?)
Exercise, everyone needs to be more active and healther - go for a walk, a run, ride a bike, schedule time to visit the Wellness center.
For the studious individuals, begin studying for finals.