I would not wear a shirt from other schools you have been accepted to or wish you could have gone to instead. That would be poor form.
On a serious note Business Casual=Snappy Casual (Vanderbilt term that I just love). For second look, now maybe this is just me, it is better to err on the side of conservative than casual (just like with interviews).
Business casual usually consists of:
For Women:
*Dress pants (black, navy, khaki) or skirt (below the knee, A-line good choice), hose usually not required, closed toes shoes (especially since we'll be doing hospitals tours, a pump, dress flats, loafers, etc), and a nice blouse, dress shirt. Think Ann Taylor (and I don't work there, but just use their "look" as a model. They pretty much exemplify business casual. There is a link to some outfits they have already put together for you!
http://www.anntaylor.com/IWCatSecti...d&Merchant_Id=1&RestartFlow=t&Section_Id=6&TN
For Men:
*Dress pants (sorry no skirts) usually navy or khaki, a long-sleeve dress shirt and maybe a tie. The tie is dependent on how conservative the school. For Vanderbilt I know that on rounds all the guys wear ties, so something to take into account.