I may surprise you by advising you DO bring a professional-looking portfolio with a legal pad. But I also suggest you actually use it to store some important items and take notes. Here's how a porfolio should be used in the medical school interview scenario:
1. Store a copy of your AMCAS application, secondary application for the school you are visiting, and any publications/abstracts in the inside folder. This will allow you to review these items prior to the interview or during breaks in the interview day. It is unlikely any interviewers will ask to see your publications, but it's not unheard of - so best to be prepared.
2. Put a small roll of dental floss into the pocket as well. I can't tell you how many times I've seen pre-meds with food stuck in their teeth when interviews occur after a meal. Having floss might just save you from an embarrassing situation.
3. Take notes! There is no need to take notes during the interview, as that may seem pretentious. But definitely jot down your thoughts after each interview making special note of:
CEO, MDadmit Medical Admissions
How to be Pre-Med
The Medical School Admissions Guide
How To Get Into Medical School with a Low GPA