What are things to wear to an interview?

I have an interview at Winco Foods (I’m not sure if they’re in every state but basically it’s a chain of grocery stores) and I’m just wondering what should I wear to the interview? I literally only own three pairs of pants which are two pairs of jeans and one pair of khakis, however the khakis are really tight on me and I’ve been told I shouldn’t wear them. I’m planning on going to Goodwill for some interview clothes, what should I buy? What kind of tops should I buy as well? For shoes I’m thinking just black flats.