When I worked as a volunteer, I tended to enjoy areas such as the pharmacy, where I could check expiration dates, or Central Supply (my favorite) where I could put together kits for the OR or barcode and organize supplies. I volunteered for those areas because on the nursing floors there was nothing to do but fill ice pitchers. I don't remember feeling like I was in the way--I just tried to make sure I was making myself useful. I would have loved to organize the nursing charts and get them in order, but didn't think the nurses would like that.
BTW, I did work in the nursery--basically you scrub up, put on a gown, and do whatever the nurses need you to do. For me, this was holding babies or restocking carts (another thing I enjoyed). I did have one baby that was hungry and thought I was Mommy! ("No, no, no, don't do that sweetie, I'm not your mommy.)