I try to eat a fairly normal breakfast on race day, and a fairly mundane dinner the night before. Hard to do if you're in a hotel, but race weekend is not the time to experiment with unknown foods.
Warm up in the water if at all possible. Gives you something to burn off nervous energy.
Empty empty empty your bladder before the race. Wee in the pool if you have to during the swim (I won't tell anyone). I know the pro's let 'er fly whenever (gross), but for us mortals trying to bike while needing to wee is a distraction you don't need.
Don't be wrenching on your bike right before the race, but I do make a short (low effort) shakedown ride the Thurs or Fri before a race. Put eyeballs on your tires & spokes for slices/damage before the shakedown ride, so you can swap a tire and still get a few miles on it for insurance.
If you have a trip odometer, remember to reset it before you go to swim.
Pay attention to the wind on an unfamiliar course. One race, I assumed the wind was out of the SW. I went bombing out on the course, just absolutely killing my normal pace and thinking "man, when I turn around and come back with the wind, I am REALLY going to fly." At the turnaround, I found out the wind was from the NE and I was spent. Doh.
If you've never opened/eaten a gel while riding, try it in advance.
Most important: Have fun!
Good luck!