I use one of these evaporative bandana's on really not days to keep me cool:
http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_93360?cm_mmc=froogle-_-350-4-12-_--1-_-38-612-908-06&hvarAID=froogle&mr:trackingCode=77A4ABC1-7B2D-DC11-8E88-001422107090&mr:referralID=NA
I didn't get mine from Bass Pro shops, but they are the same thing. I got mine years ago from Bassarama. They sell some cheaper ones at Wally World, but they don't work as well. The one from BPS is the same as the one I use - just a different color - mine are plain solid colors.
I drink tons of water, as well as gatorade. I eat energy food during the day. If I feel a headache coming on, I grab a solid chocolate bar (not a snickers or anything like that - just pure chocolate - hersheys) and scarf the whole thing down, followed by some water.
I take daily vitamins from GNC - the "mens pack" vitamins.
When the weather gets as hot as it's been lately, I skip the morning coffee. I just drink a big glass of OJ, or down a few gatorades before the sun gets up.
Eat breakfast - no donuts. No "quick" stuff. Get up early, make some eggs and toast or something like that. At the very minimum... I'll eat a big bowl of Honey Nut Cheerios and milk.... but if I can, I'll eat a real breakfast.
When I lived in Florida, the club I fished with wouldn't think of going out on a empty stomach - we all stopped at "Huddle House" (like a Waffle House) and ate a full breakfast before heading out.
BTW.... I've seen your skin tone. I know you like the sun. Start slathering on the maximum protection BULLFROG sunscreen. Leave the "suntan lotion" at home. Put "sunscreen" in your boat, and use it. Before you leave in the morning, put it on your back and chest before putting your shirt on too. Think that material blocks all of the UV rays? Nope! You can get skin cancer in areas your clothing covers just as fast as uncovered areas. I had a friend in Florida that never fished in short sleeves / short pants. He had these lightweight white shirts, with matching pants - thin material, very lightweight. He always wore long sleeves and long pants, and I hardly ever saw him sweat. I guess it's all in the material.
I feel for ya' brother. I hope some, or all of this, might help.
All the best,
Glenn