I'd advise semi-casual, like maybe a nice pair of jeans, or even slacks. Pair it with a polo shirt(solid color, no stripes). If it's a girl doing the interview, a nice blouse and some nice jeans should work(and minimum makeup).
Just a clean collar shirt and slacks. To be safe until you're hired wear a long sleeve shirt for the fast food if you have a lot of tattoos. Never know! i don't think the Gas Station would matter much though.
You should dress like you were interviewing for any job. Clean, wrinkle free nice clothes. No jeans! If it comes down to deciding between two people for a job most employers take notice of one who shows respect for themselves and others. Also pay attention to details like your overall appearance. Neat hair, clean hands and fingernails. Always put your best foot forward!