Step 1, clinical grades, letters, and research are what's most important.
Community service doesn't matter too much, but, obviously, volunteer if it makes you happy.
Most med student clubs are pointless, but having some leadership role is probably somewhat helpful and it may give you the opportunity to network with some important clinicians.
If I did it again, I would try to pick a speciality by late 1st year, and then gear my entire application to that field. I'd become an officer in speciality X club and maybe try to get involved in the national organization for speciality X, I'd do a summer research fellowship between ms1 and ms2, and I'd try do a project during ms2. I'd then try to write a case report or 2 during 3rd year. I don't think what I described would be that much extra work.
In reality, however, your step 1 is pretty much all that matters. My application was pretty sparse and I still got 40 something anesthesia interviews based mostly off of my step 1 score.