Energy gels are great for ultra-running, as they provide the lightest possible nutritional support.
To do this, they start with sugar. Sugar is the fuel your body runs on, and specifically, the sugar “glucose”. As you exercise, your body uses up its ready supply of glucose, and starts burning other things for fuel. It breaks down fat (hurray!) and also muscle (doh!) and starts to use these breakdown products instead of sugar.
Just eating glucose isn’t practical for ultra-running. One would have to constantly consume small amounts of glucose to prevent big spikes and troughs in available blood glucose (sugar rush, then crash).
To even this out, energy gels use starch. A chain any simple sugars is called a starch. A starch of only glucose sugars is called “maltodextrin,” and that is what is found in energy gels.
One’s intestine breaks down starches slowly (simple glucose may be absorbed directly through the stomach into the blood, most of it doesn't even make it to the intestine). This results in blood sugar going up in a more moderate and sustained way as maltodextrin is broken down into glucose, and absorbed.
Energy gels combine maltodextrin with a simple sugar called “fructose,” which is very similar to glucose. Fructose is added because it tastes sweet and also because your intestine absorbs a mix of sugars better than a single form. You will be familiar with a sugar made from the combination of one glucose and one fructose, it’s a sugar called “sucrose,” the one we extract from sugar cane and put in our coffee.
For ultra runners who need to replace energy but don't want to be slowed down to eat, this formulation of maltodextrin (glucose starch) and fructose makes a lot of sense. They can easily get a mouth full of energy and keep running. But it’s not health food. It’s a mouth full of starchy candy syrup.
This starchy candy syrup is fortified with: some electrolytes lost in sweat (sodium and potassium), along some amino acids (the break down products of protein), and some anti-oxidants (like vitamin C) because endurance exercise creates lots of free radicals, which anti-oxidants stabilize.
This would be great if you were trying to run an Iron-Man, where seconds lost eating count. But you’re trying to hike for a day straight, covering 50 miles. For that, what you are eating: mainly starchs (pretzels, banana, granola bars, etc.) with some fat and some protein (chicken salad sandwich) is perfect (as long as the mayonnaise doesn’t spoil and make you sick). Keeping some jelly belly beans (being almost entirely sucrose and glucose) handy sucking on them one at a time would work just as well for you as an energy gel.
I’m not certain how many calories you are going to burn in this endeavor. The Leadville 100 mile ultra race calculates competitors will burn 12,000 calories covering twice this distance in half the time. Those competitors are moving faster, but carrying almost nothing for a supported race, so it seems calling those factors a wash and cutting their number in half is a reasonable estimate. That means you want to consume about 6,000 calories, and up to 2,000 of that can be basically junk food: candy, chocolate, pretzels… Why not enjoy it rather than choking down an energy gel.
I do use endurolyte tablets when I run longer than 5K. And they may be helpful for you in this effort. Endurolytes include the full range of electrolytes lost in sweat, rather than just sodium and potassium like most energy gels.
A multivitamin before, in the middle, and at the end might also be useful.
For your water requirements in this endeavor, your goal should be to start well hydrated, and finish at the same weight as you started. If you weigh more at the end, you may have consumed too much water, and if you way less you have consumed too little. Try bringing a bathroom scale with you on your Saturday prep to see where you are before and after.
For more research, I’d recommend you read articles and advise on the Leadville 100, taking the considerable amount that is written on training for and running that race as good advice for your own plan. Not just on nutrition, but also how to pace the course for the best time, etc.
Finally: Good on you! This sounds like a great idea for an adventure course. Please let us know what worked for you and what didn’t. I’ll never run Leadville, but I can see myself trying and something like this.