Since you have no appreciable healthcare experience and you want to pick probably the most specialized of the mid-level provider professions I would shadow in the OR for as long as you can. This shows that you have a more in depth understanding of what you are trying to get into. Bringing grandma dinner trays and greeting people at the front door is pretty much worthless. Sorry, but if time is limited I would shadow more and not volunteer. Don't get me wrong volunteer work may make you a better applicant, just that shadowing will most likely look better.