Get plenty of rest. Eat well, sleep well, and stay relaxed.
Review the basics - redo problems you've already done in the past, and focus on getting them right quickly and with confidence.
Maybe do some easy-to-medium difficulty new questions.
Review your timing plan, how you're going to organize your scratch paper, and which strategies you'll use for different types of questions.
Don't waste your time studying new concepts at this point. When you do that right before the test, here's what happens - you start a problem, realize 'hey, I just learned a strategy for that', and spend way too much time trying to make it work, since you haven't had enough practice yet to make it quick and automatic. Then you're short on time, and if you got the question right, you now have to face even harder questions...
Focus on maximizing the score you'll get with the ability level you have now. That means going into the test feeling great, and ready to avoid careless mistakes and fully use what you know.