On serious point for the OP, I think the main thing is a positive attitude, and some evidence you have already been taking an active interest in the markets in some way. As I understand it a lot of the intern programs are rotational, so there's no way someone still at Uni is going to have much technical knowledge. All they're gonna have is a bunch of book learning at best, and that ain't worth that much on a trading floor. So smile, be relaxed, and don't come across as a pain in the @ss.
Try to sound well read as well - theres every excuse for not being able to talk fluently about vol skews and their impact on gamma profile, but no excuse for not having time to read the economist etc. Time is the one thing you probably have more of than the people you're interviewing with. So make sure you don't come across as spending it all in the bar.