I personally feel that EC's are overrated in the admissions process for your run-of-the-mill applicant. If you have done something above and beyond, like Peace Corps for example, it might make a difference. Other than those special situations, every applicant is going to have fairly similar EC's.
I didn't decide I wanted to go to medical school until right after I graduated from college. I took about 1.5 years off and worked as a research technician at a medical school. While working, I would volunteer a couple nights a week at the university ER.
That was really about it. In college I didn't do a whole lot except eat, sleep, get loaded, and study a little. No school paper, clubs, honor societies, fraternities, leadership stuff, etc. And I was single with no kids.
I think EC's are more important to applicants who don't have strong "stats". For those who may be on the borderline of gaining acceptance, some really impressive or unique EC's might make the difference.
btw, volunteering at an ER (preferably a university one) one or two nights a week is a great way to prepare for medical school. You can pick the brains of the residents and attendings about medicine and medical school, you get to see a lot of cool stuff, you get to "shadow" docs, and it counts as volunteer experience.