I agree with the posters above. I think it's really important to find something that you really enjoy, it will make your experience a lot more pleasant.
To answer your question more directly though, I had no experience working/volunteering in a clinical setting and wanted to find something that would help me really understand what healthcare is all about & provide patient interaction. I chose to sign up for AmeriCorps Community HealthCorps (AmeriCorps has a lot of programs, but this one is tailored for those interested in healthcare for the most part).
Not everyone that was in my group loved it (its an 11.5 month program, crap pay/stipend, fulltime hours, etc), but I really enjoyed my experience. I learned a lot and was able to have the direct patient interaction I was looking for (1st yr: helped uninsured chronically ill patients enroll in pharmacy assistance programs for free meds & also did health ed outreach work, 2nd yr: reproductive health educator @ an inner city school based health clinic). I was able to shadow a bit as well since my placement was based out of a hospital & community clinic the first time around.
If a program like that is not your thing, there are tons of other things out there that I think can provide a valuable experience (volunteer at a community clinic, street outreach, ER volunteering/translation (if bilingual)...I've even heard of being an ER medical scribe can be good.
Just make sure you choose something that is right for you and will strengthen professional and personal skills.
Good luck!