And the answer is…none.
The college application process, including the applications for BS/MD programs, is pretty much on the honor system. Colleges ask for specific information and they trust that students will be honest in providing that information. Because of that, you will virtually never need a letter from a facility that you volunteered at confirming the number of hours you worked. Similarly, you don’t need a letter from a doctor that you shadowed that describes what you did and for how long.
I can see the questions forming in your head already. If no documentation is needed, what is to prevent some unscrupulous student from lying about their hours or what they did?
Several factors are in play here. First, although colleges have never made documentation part of the application package, they have the right to request documentation if they suspect that something isn’t right with the information they receive. And given the thousands of applications that most colleges are reviewing every year, they tend to get pretty good at figuring out what isn’t true on an application. If they discover you have lied, your application will hit the trash can.
Second, colleges with questions about the truthfulness of an application will often contact the guidance counselor for the student. If it is something significant on your resume, the odds are good your counselor would know about it. And if they don’t, they can certainly ask around to find out if you were being truthful.
Third, never underestimate the power of competition. There are hundreds, if not thousands, of stories of a student reporting their classmate for lying on a college application. Sometimes this happens before decisions are made and sometimes it happens after a student has been admitted. If a college finds out that they admitted you after you lied on the application, they will withdraw their acceptance.
Bottom line? Just be honest and you have nothing to worry about.