Biggest MCAT advice I can give:
DO NOT, UNDER ANY CIRCUMSTANCES, PAY ANY ATTENTION TO ANYONE IN THE TEST AT ALL!!!!!!!!
They'll psych you. Be like a prize fighter, stay quiet and contained. If you have it, take along a walkman with some music (no lyrics, don't want lyrics in your head during the day) and just sit quietly and listen to music during the breaks.
To get to the bathroom, be one of the absolute last people to go into the test room on the day of, because they'll sit you all from the front back. So you can be first out the door when break time comes.
Stay hydrated and alert. Chewing gum is thought to keep the braina little snappier. Eat a good breakfast, oatmeal with raisins (raisins have a high boron content, which has been shown to improve memory), and some protein like eggs. You have to eat before the test, or your score will dip because baby, this is a long test. Don't want to crash out. And eat a really healthy lunch, with both protein and carbs (complex, not simple. Stay away from candy all day. I suggest a bag of fruit and nuts with maybe some M+M's thrown in, that'll hold ya real well).
Relax. It's not so bad. Just really consciously take really good care of yourself. Oh, and start stocking up on sleep TODAY. 👍