How to dress when you go to an organization is very important. You are representing your institution as a whole when you volunteer with another organization. Some of these links are from specific organizations but the guidelines are applicable to your institution as well. Keep in mind the conditions of the organization you are volunteering at (such as outside, inside, etc) and what rules they have for your attire.
This path will give you a full understanding of the responsibilities required for this position as well as teach you the skills required.