Had to jump in on this one. Pardon the health kick I'm on, but if you want to get serious about replenishing electrolytes and maintaining energy, here are my following recommendations. I feel compelled to write because I'm also a triathlete and push my body to the limit on a daily basis.
1. Water + a good orange.
2. If you've been fishing hard all day, make sure you're getting your salt too. It helps the water absorb better.
3. Bananas help too--great source of potassium.
4. If you want to fish harder and cover more ground, try one of the althletic supplements.
I take one called Carbopro. It's complex carbohydrates. I take a scoop of this with my water. It absorbs easily, very easy on the stomach, and bottom line is you'll kick butt.

Mountain dew is horrible. Gatorade is not the best, as it contains a pile of corn syrup.

I'll get off the podium.
Fishingking