I worked for the
Disney Store about 4 years ago and the number one thing I would suggest is that you not take the job "for the money". Sure it's fine to say you're looking for "supplemental income" I'm not suggesting you lie or anything but really they wanted people who were looking to be part of the team. People who had a vested love/interest in Disney and want to be part of that family.
Standard Interview Questions for any job might be:
Why do you want to work here?
What skills do you bring to this position?
What is an area that you could use improvement in? // What are some of your weaknesses?
For your interview I would suggest a "professional" look. This is always appropriate for an interview even for a casual position. A suit, or nice dress pants/top etc. But if you have any Disney accessories (small Mickey earrings, a watch, etc) that's a way to subtly let your love for the mouse show.
If you can show that you fit the Disney "look". neatly combed hair, natural make-up, no visible tattoos, etc that will help as well.
Smile! That's important, try to relax and I'm sure you'll do fine.