Typically, I would stay for winter session (3.5 week class) before the Spring session began and the Spring tennis season started for me. I'd go to class for few hours, workout or do indoor tennis drills with my coach then go back and study then go out and have some fun. Here were my filler courses:
Sophomore Year - Human Sexuality which included class interviews with prostitutes, priests, transsexuals, etc..
Junior Year - Investments. This was not a blow off course and I don't recommend it if you want to have fun
Senior Year - Economic Geography. Awesome class.