Come armed with a question. Interviewers usually ask if you have one. Most applicants hem and haw and finally say that, well, maybe the tour answered them all. A good question generally deals with the character of the college: "What kind of student does best here?" or "How is this college different from other similar ones?" A good question takes thought and is evidence that you've done homework. Dumb questions can be answered on page one of the catalogue ("Do you have a business program?").
It is not usually necessary to bring a transcript. Your high school will send an official one if you apply. Exceptions, however, include students who want to explain an issue in their record, or who would like a seat-of-the-pants assessment of their chances for admission. If you would like to show a sample of your art or poetry, feel free. Slides or tapes are also a possibility, but be sure to verify in advance that such things can be accommodated.
When the pre-interview jitters hit, keep reminding yourself that the interviewer is your friend, or at least wants to be. No fear. No pain of rejection. Just a sincere conversation.