Here's my funny take....but it will take a little explanation.
Sometimes before a trip to FL, I try to shed a few pounds (knowing I'll probably add a few while in FL). The easiest way for me personally to drop a few pounds is to cut all the carbs for a week or two.
I don't do this diet every trip, but when I do, my ride endurance/tolerance goes up significantly, at least until I have carbs again.
One 'diet' food that works really well is chia seeds. They are bit hardcore to be certain. I don't know the name off the top of my head, but one company sells pure chia seeds in little packets called "chia shots." The packets are orange, and very portable. They are also high quality chia seeds. Some of the chia seed brands I've tried are kind of bitter, and often chia seeds are pared with high sugar.
Chia- is what the Inca messengers ate when they wanted to run up mountains carrying messages. They are full of good nutrients. (Also, as part of this diet, sauerkraut and kimchee are super.)
Unfortunately, the ride tolerance benefit wears off as soon as I start eating all the high carb theme park treats.
Prior to finding chia, I saw the same benefit if I stuck with just protein at breakfast, but my food of choice was eggs. I've not found much else that is carb-free for breakfast at WDW. I can't even find plain yogurt.
