Here's some. If you got others, post them:
Hydrate the dry before, start the race well hydrated, hydrate throughout the race. Don't overdo it to an extreme tho.
Electrolytes tablets in your water bottles.
Protect yourself from the sun. Wear a cap or visor to shield your head, face, and eyes from the sun’s burning rays.
Don't forget your sunscreen.
Don't forget your sunglasses.
You could put ice cubes in your hat.
You might adjust your pace to the heat.
Go heavy on the body glide to prevent chafing on the bike/run.
Use the spray stations along the course, if provided, and at the finish to cool off.
Some extra salt on pre-race food perhaps.
Eat your electrolyte-intensive food: goos, banana, etc.
If wetsuits are banned: you may not float as easily, you might be somewhat slower, but you'll have freer range of arm motion.
Here's some more:
For quick and refreshing recovery, make sure to stop by the DC Triclub tent and cool off in one of our 2 state-of-the-art kiddie pools, filled with ice, compliments of Ryan Troll. Even more incentive to race fast and finish early: the pool temps (much like the air temps) and the sweat-to-ice ratio will both go up precipitously as the day wears on!
There are also rumors circulating about a possible slip-n-slide... but news sources (mainly this message board) have yet to confirm these sneaking suspicions. Personally, I'd like to see the slip-n-slide run the last 10 meters of the course, stretching across the finish line (thus helping people build up speed for the Blazeman roll! That would make for some great race pics (particularly if there is a photo finish!)