You'd want to read the mission statements of schools you plan to target to get a clue as to what they value. Besides volunteer work, both clinical and nonmedical, physician shadowing is good to have. Aim not just for research, but possibly posters/presentations and/or publication. Leadership and teaching also benefit one's application. You'd also list employment and hobbies/avocations, Honors/Awards/Recognitions, sports, and artistic endeavors.