Depends on the program, but I wouldn't show up initially in scrubs. They will usually take you to the OR change room to get scrubs when the time comes.
Start with at least a shirt and tie, with some nice shiny shoes. Bring a change of comfortable shoes for the OR, and definitely bring your own lab coat. Keep a pen on you at all times.
If you really want to impress, wear a man-thong, so you can let a little bit of the T-bar poke out when you bend over. You know, show a little slut-butt.