This is the list I made of stuff to dring:
Leather portfolio - with pad of paper and pockets
Pen
AMCAS App
Secondary App
Honors Thesis (if you have one) or any publications
Breathe Mints/ Floss (good idea stolen from Law2Doc)
Have a few facts about the school jotted down
Have a list of questions about the school (general and specific)
Money
Before going to the interview (some of this can be done in the plane):
1) review your secondary and make sure you are prepared for EVERY questions they could ask you
2) go over your college transcripts and make sure you are ready to explain any problems in it (C's/P's and W's). Remember B's are good grades so if they ask you about a B don't feel the need to explain it away.
3) Quickly jot down any recent books you have read, and you favorite alltime books, and any journal articles you know pretty all (as a plus, if you find an article by someone on staff at the school you may want to read it, print the abstract and bring it with you to reference)
4) If you have pictures of yourself participating in some community service activities or academic events (things that are special so no Graduation photos, nothing Greek, and nothing with RA/Student council stuff, think volunteer work or working a lab or presenting at a conference) you can bring these and hold onto them. If you get the opportunity, mention that you have them but DO NOT pull them out. If they want to see them then they will tell you. Only mention them if the activity in the pictures actually comes up.
GOOD LUCK
and stay relaxed. My friend gave me a tip to relax that I really like (she used it to get into UCLA and Yale Buisness school). Think of a really ridiculous song (I have a person list if you want some suggestions) and then get it stuck in your head. When you are sitting and waiting for your interview it will be harder to get ridiculously nervous if your thinking "I've got a lovely bunch of coconut deedle lee dee"