Pretty much everything -- I managed to draw my shirt/gun - load my shirt/mag and toss a mag on the ground during the event (I call it an event, as I managed to give everyone some good laughs)
The shirt I was wearing was a button up, and went about 7-8" past my belt line, even will a full grab with my left hand I was not clearing the gun all the time.
Todd and others made some remarks about suitability of clothes.