Okay, here's what I did, it may or may not help you:
About four weeks before the test, I started taking full length practice tests on Saturdays, at the same time the MCAT would be. That way, when I was at the test, it just flowed like my practice tests. I was used to it, and didn't think about it too much.
But I was still anxious a few days before the test, so I made a special "get psyched for the MCAT" CD, which I listened to on the way in the car, and as I walked to the test. It really helped me focus and get ready to take on that mother of all tests. It may sound cheesy, but "Eye of the Tiger" really is the best for this sort of thing.
Also, take protein bars for breaks. That way, instead of spending that time thinking about questions you may have answered wrong or worrying about the rest of the test, you can spend that time thinking about how awful those things taste.
That's what I did.
Also, and this is pretty important: don't talk to people. at all. you'll hear about all the people who studied 5x as much as you, you'll see people cramming for the test, and you'll worry that maybe you should be cramming, too. You'll lose your focus and get more nervous. So keep listening to your music or special CD. Keep focused. Get in the zone.
Don't cram. It'll make you more nervous.
Okay, I think that's about it for my strategy. Do with it what you will.