Between 14 green and 15 tee in the afternoon round the beverage cart came around and I grabbed a Gatorade. I remarked to the caddie that by that point, 10 hours into a 10-1/2 hour day, I was basically drinking it so I wouldn't feel bad at 9pm. Much too late in the process to make any difference on those last few holes.
I think the three best things I did yesterday were 1) downing a 32oz. Gatorade at 5:30am before breakfast, 2) taking a second set of clothing shoes-socks-underwear-shorts-shirt-hat head to toe for the afternoon round and 3) eating a not-too-big lunch between rounds.
Nothing will bring a hot outdoor day to a quicker end than chomping on a burger and fries when you're already a little overheated, then stepping back into the sauna. I've only done that once. Never again.
But hydration is the key. And bananas, even though they get kinda squishy after a few hours in the golf bag. And never underestimate that restorative powers of clean, dry socks and pants.