I have an interview at Goodwill on Saturday what should I wear and what to expect?

I applied for a cashier position and I was called in to take a T/F test which I obviously passed being that I have an interview on Saturday. My question is, what should I wear to the interview? would I be able to wear open toe wedges? ALSO what kind of interview questions consists in a cashier interview at the Goodwill? I want to be very well prepared as I haven't had a job in 4 yrs minus the one I had with the Census bureau for a month.