jefgreen,
Volunteering, or working in the medical field is a great way for you to beef up your medical school application. In my experience, anything that you would do, that would show that you have a true intrest in the medical field will benefit you.
EMT...etc: I was an EMT-P in PA prior to growing up and going to Med School. Infact working as a medic, was the reason that I went back to school, but that is another story. My experiences in EMS allowed me to develope what I think is the most important aspect of medicine, patient rapport. I mean think about it, you get off the ambulance, meet a patient, and in5 min or less you have to instill trust, that you will care for the patient, in the worst time of their life (assuming its a true emergency). Anyone can learn the book stuff, its the people interaction stuff that makes you a good Dr. I would highly endorse the idea of doing the EMT route.
Other fields: similar comments here. Anything that will get you to talk with patients will benefit you.
Research: Yes, if you have an intrest in research by all means go for it, even better, if you have a personal reson for wanting to do it. I had a friend who did research on cystic fibrosis (CF) because she had a brother affected by CF. This experience that she got doing research really showed her commitment to medicine.
in summation, anything will benefit you, just get out there and get around patients. Candy-stripe and just go talk to patients. Become a nurse aide, vol at a nursing home, etc, just get out there.
Hope this helps
Kevin