Exam certificates and any other certificates you have. Any reference letters/reports from work experience placements. Bascially, anything to show the interviewer what a fabulous person you are.
Now might be a good time to start putting together a CV too! :-) May as well start young, and add to it every few months, rather than having to do the whole lot when you leave college. :-)
Write it on the computer, save it, back it up, print it out!! CVs are SUCH a pain to get right, that's why I advised starting early and building up! By the way - good luck with your college interview! :-)