Bring two lengths of garden hose, 50 feet each. You'll need them.
Garden hose nozzle is a good idea.
Rolls flat garden hose is kewl.
Four way faucet keys are a good thing, I've got to buy a couple. Vise grips aren't just for exhaust systems.
Galon garden sprayer is a good way to apply coil cleaner.
Check your watch. Let the stuff work, don't be in a hurry to rinse it off.
Tylenol is a good thing.
Nice to work on a building with water fountains, so you can drink lots of water.
Ninety degree days are rough for working outside. Roofs are worse. Black tar is not your friend when it's ninety degrees.
Ice cubes and reconstituted apple juice is a good thing when you get home.