students on away rotations are primarily judged upon work ethic, character, interpersonal skills and knowledge base. we don't care if you can operate or put in a central line; that's what training during residency is for. if you are technically skilled, that's great, but we're more interested in what kind of person you are and if we think you'll fit in.
as far as "doing stuff," it depends on the rotation, the resident, the attending, and the institution. i let medical students put in central lines and help in the OR, especially during closure. once, i talked a second year student through a tumor resection. she did the whole thing.