I'm going to offer you a different perspective than some of these other people.
I was actually relaxed when I studied for the MCAT. It was when I wasn't doing anything that I started to think about it. I'm actually a big fan of routines. I study in the same place, usually at the same time. I eat/drink the same things when I study. So for me, quitting cold turkey right before the MCAT would have been dumb.
My advice: If you have the Kaplan flashcards, go over those. Just quiz yourself over them. It's not stressful, and if you're not sure on somethng, flip through your book and take notes on that whole subsection and understand why you didn't know that answer. This really solified things for me, and I scored about 3 points higher than my practice test average on test day.
What else? If you're planning on drinking coffee before the MCAT and you're not a regular joe drinker, you may want to think twice before you just jump in and start drinking. It might give you the jitters, it might make your mind race, and it might keep you up at night. Start drinking at the very latest now if you think you may have a problem clearing the cobwebs on test day.
Also, on the rest thing, make sure you get sleep the night before the night before (i.e. two days before your exam). A lot of people are just going to have problems falling asleep the night before. Make sure that it won't drastically affect you if that's what happens to you by building a "sleep reserve" throughout the week.