In the last year of high school had a free period before lunch, giving me a total of 2 and a half hours to sit around and do nothing. Since one of my friends lived 5 minutes from the school we would generally just walk down there and sit around, while playing videogames and eating leftover food.
In university, however, the nature of scheduling means that my schedule is riddled with holes and spaces between classes, so I usually either go back to my dorm, or go and get lunch or to the library, depending on how much time I have to kill.