What are fun team- and trust-building exercises?

I attend a career-based high school and the schedule is set up where we have four base cles and one three-hour lab. So since junior year (I'm a senior now) this cl has become really close and tight-knit. Lately, though, a lot of drama has separated us, and all we do now is bicker and fight amongst ourselves. The leaders of the cl are thinking about having a girls' weekend retreat so that we can repair our relationships, but we're having trouble coming up with different exercises to rebuild trust. We'd also like to have a session to nicely say what problems we may have with another person, constructive criticism, but without hurting feelings or stepping on any toes. Any ideas on how to do this? I'm afraid if we don't do something now, the problem will only escalate into something terrible later.