Even though extracurriculars will not make or break your residency application, it will give you something to talk about on interviews, allow you to network, give you something to bring up in your personal statement, and will be impressive to your letter writers.
I'm not saying you have to join every ultimate frisbee team or sushi-making club on campus, but volunteering at a free clinic occasionally (and even being some sort of "coordinator") may ultimately help you. Or if you're going into primary care and volunteer at a health fair or to teach kids in school. I volunteered for probably a cumulative 8 hours/semester, and people were always impressed with how "selfless" I was, and I know my letter writers took notice of the fact that I wasn't just going to school and home every day.
Not required, just food for thought!