Well, I think the reason they have a rep is usually to make it easier and more convenient for new students to get all their shopping done in one fell swoop, but you have to be careful. Some places give a discount to students, others charge a little more as a fundraising opportunity for the school. If you don't know what they'll have available, it makes the choice more difficult ahead of time- if they only offer one type of scope, for instance, you might end up buying one you wouldn't necessarily choose if you were shopping on your own. If the school REQUIRES you to use a certain type of instrument, this is a plus because you can get it directly from the rep when they visit. As I understand though, you have to order it- they don't usually have the stock on them. I've read here that some students have complained that it takes longer to get the items, or that they won't get them until the first week or day of classes. So, it all depends on what your school requires and how soon you need the items, really.
If they've given you a list already, there's no harm in shopping around. Personally, I wouldn't buy a stethoscope without testing it out and looking at all of my choices, but as a first-time student it may not make much of a difference if you don't know what you're listening for. If you've never used a stethoscope before, you won't know what you're evaluating...does that make sense?
If you already have your list of items, you could post them on here and get suggestions, or go to a large uniform/supply shop and see what they have in stock...do this before the rep visits so you have an idea of prices before you have to make a decision.