If you are already shadowing a doctor, keep doing that. If you do not like your hospital volunteer position, find something that is more meaningful to you to get experience. I volunteered at a free clinic which served the uninsured population. Most of the patients were homeless, had severe mental problems, or were just unable to afford insurance. I loved learning about a more about the insurance issues in our country and I learned how to handle delicate situations.
Also, do some volunteer work (non-medically related) you love if you have time. I have coached a girls basketball team the past 3 summers just for fun. I also am part of a program at my school which advocates being tobacco-free to middle and high schools students. We get to go do presentations at school and interact with the kids. I love it because I feel like I am actually doing something. I would not suggest doing an extracurricular activity just for the resume, because in the end you won't be able to talk a lot about it at interviews and you are just wasting your time.
A lot of my friends do Best Buddies. Also, look up camps in your area where you might be able to volunteer to be a counselor for a week or weekend. I did this at Camp Boggy Creek in Florida, which is for kids who have a chronic or life-threatening disease. I had a blast and those kids made such of an impact on me. These types of camps exist all over the place, and most of them don't charge for attending so they need volunteers, a lot of them.
Sorry for the long post, but I hope this helps!
