Several schools I applied to, were separate MD and PhD programs. I did not have one minute of volunteering or candy stripping or shadowing of physicians. I had no clue that it was important and it wasn't something that I did naturally. And frankly that is the case...what you actually like doing and have a passion for is most important. If you begrudgingly go to a nursing home once a week and hate it, that will show on your application, even if you've been doing it forever. Admission committees are not stupid and can instantly see through applicants that have done something, just to stick it on their application. Do it because you want to, not because you feel like you have to.
And certainly don't post how much you hate volunteering at the after school program for blind children on your Facebook page.
- my 2c