I've been messing around with this lately and have found some things that work well for me.
Number one most important aspect of pre-meet nutrition: Dont use or do anything new. If you havent been taking or eating it during your training dont start now. You have no idea how you will react.
That being said, here is my full meet day nutrition. I am not saying this is the end all be all but it works well for me:
With breakfast, which is usually some scrambled eggs and coffee if I am watching weight: Centrum, 3g Kre-Alkaline, assload of vitamin b, and no liquids, other than coffee
Immediately after weigh-in: gallon of 50/50 water gatorade mix, shitload of bananas, more vitmin b, 3 more grams of kre-alkaline, rockstar recovery mixed with couple scoops of Surge Workout Fuel (keep this topped off all day, probably go through about 3 cans and 6 scoops and have yet to test positive for caffiene), 3 scoops of protein powder in water, lots of fish oil. Fair warniing, your pee will be two things: constantly streaming and glow in the dark/neon colors at this point.
After Squats: 3 more g kre-alkaline
After Bench: 3 more g kre-alkaline, more bananas
After DLS: try to get another shake in and at least another bottle or 2 of gatorade. Then a ridiculous victory meal.