Back to school outfits? Please Help!?

I'm going into 7th grade this year. I'm going to a new school this year. It's a private catholic all girls school. We do have uniforms but the first day of school is a casual day. I've gone to private schools all me life that require uniforms so I've never worn causal, everyday clothes on the first day. I don't know what to wear. Please Help! P.S. My favorite stores are Hollister and Abrecrombie & Fitch.