It's not imperative that you join any clubs, as long as you have other meaningful EC's. Your hospital volunteer and EMT job are great clinical experiences, research is good, and the CPR classes sound cool. It's not necessary that you join any clubs, although I think a lot of students join them because they're fun AND they can provide good leadership opportunities, which many top schools like to see. It's better to have a meaningful role within one club than to just be a random member in a bunch of clubs. So join another club if it interests you and/or you'd like to run for a leadership role, but don't do it just to do it. Hope this helps.