While I think extracurricular activities are nice and all I think the best thing you can do is study hard and do very well on the MCAT. I would focus on that first. I think the schools weigh academics more than outside activities you are involved in. With that said I did volunteer in the ER (along with other ECs) but they never asked me about any of that in my interview. You could spend some time doing something in the community, and also try to spend some of your extra time shadowing and/or volunteering in a health care setting if possible. Just my 2 cents.