I respectfully disagree with the suggestion to wear a CAP uniform to an interview for a non-CAP activity. A CAP cadet myself, I have heard all sides of this argument, but will caution against it. It could create confusion as to what organization you are a part of, and has backfired in a few instances I know about. An alternative is a CAP lapel pin or tie bar/tack. That is all I will say about that.
Interview tips: Take your resume and a notepad even if you don't think you will need it - be prepared. Also, have 1 or 2 intelligent questions to ask the interviewer(s). These should not be simple (what is Boys State like?) but a little deeper. Dress professionally (suit + tie) and your counselor said it best: be yourself.