What do I wear to the interview?

So I have an interview tonight, its nothing fancy just one of those new self serve frozen yogurt places. I've never really had a formal interview before so I'm not sure what to wear.

at first I was going to wear an appropriate dress, but now I don't really feel like it :P instead of the dress I was thinking khakis, and button up shirt and for the shoes, my Sperrys. do you think that's too casual?

help!
What do I wear to the interview?
Post Opinion