Take a last practice test or two, but don't overdo it. Too much prep will stress you out.
Review strategies and question types for difficult sections
Keep studying your math and vocab flashcards
Go over your example bank for the essay
Double check your test day materials ahead of time
Get 8 to 10 hours of sleep each night
Eat healthy and relax!
The Official SAT Study Guide (Paperback)
This is the only book with practice tests that are actually written by the creators of the SAT. In other books, we have come across occasional mistakes and the questions aren't quite the same as the real test. Without a doubt, these are the most realistic practice tests available.