This kind of question is just personal experience. I don't think it would help you much for someone to answer it for you, but I'll go ahead because I like talking about myself.
My role (and for the rest of that course sadly) was being the leader. Calling the shots -- and taking the blame for when things went wrong. The first activity in that class was a teambuilding exercise where we had ten pasta sticks and five marshmallows and a set amount of tape. We were told to build a tower in twenty minutes out of the materials given. Since I had already did the activity in another class (it's not very original) I led my group to do the exact same thing I had done before, already knowing the flaws. We won the challenge and got candy like little kids.