To answer this question, we can refer to one of the conversations Montag has with Clarisse shortly before her death.
In the conversation, Montag asks Clarisse why she doesn't attend school; Clarisse answers that she has been classified as anti-social and that she doesn't feel as if she fits into an environment where students are expected to absorb information without benefit of discourse. She complains to Montag that most students are so bogged down with copious amounts of seemingly useless information that it is all they can do to survive their school days.
In their free time, the young people focus on letting off steam rather than on indulging in constructive hobbies. For example, Clarisse relates that most of her fellow students either go to bed after a long day at school, go to the Fun Park to pick on strangers, break windows in the Window Smasher booth, or wreck cars with a wrecking ball at the Car Wrecker venue. She says that other peers often play a dangerous game of 'chicken' by racing their cars and seeing how close they can come to lamp-posts before self-correcting.
Clarisse says that she is different from her peers. She confides in Montag that she is fearful of young people her age because too many young people die at each other's hands. Also, since many of them drive irresponsibly, quite a few die in car wrecks. She herself prefers to ride the subway trains and to watch people as they come and go. Sometimes, she even enjoys riding the jet cars at the Fun Park. Although she also likes to listen in on other people's conversations at soda fountains, she is disappointed that most of them engage in very shallow conversation. The discussion ends with Clarisse complaining that all the museums carry nothing but abstract art; she relates her uncle's words about it being very different in the past. Because of her uncle's wisdom, Montag comments that he must have been a very remarkable man. Clarisse agrees with Montag, and they soon part ways.