Is there anything wrong with bring a backpack to an interview?

Question

I am going to an interview for a fast food restuarant.

Answer 1

Only if your interviewing to be a bicycle courier.  Otherwise leave your c**p in the car.

Answer 2

Well personally I like to be over-dressed than under, and a backpack is too casual and informal for a job interview, even Fast Food.

Is that enough to keep them from hiring you?  Not necessarily, but if there are other applicants, equally qualified, who give equally good interviews, who have a more professional appearance, I can pretty much guarantee you the backpack would cost you the job.