I dont know that they know where they are going, and the producers must be seeing to it that the pair doesn't pick the same tool. They surely do waste a lot of time/effort on making shelters (that don't do much in the way of protecting them from anything).

It would be much better if they were allowed to tell each other what they picked as their "one tool" and if they knew what area they were going to. All you'd really have to do for 21 days, in a place that doesn't get really cold, is assure yourself of a safe water supply, and something like a 2 poncho tent to wrap up in, preferably with a removable, heavy duty Mylar Lining. Nobody chooses a water filter as their "one item"? I'd much rather have to make a knife by knapping flints than have to build a shelter. All of their shelters have leaked, provided no protection from bugs or animals, and all have fallen apart if much of any wind blew there.
You can go 21 days without eating, if you are just lying around. But that wouldn't make an interesting show. If you knew that relatively hard rocks can be had there, a 1 gallon carbon steel cookpot with lid would be a good choice. Sharpen one side of the lid, and it's a knife. Strike sparks off of it with a rock, and you've got fire. Boil water in it for safe drinking, and of course, carry water in it and cook with it. If you've got the pot and she's got the ponchos/tent/mylar, your only issue is dry tinder, and a chunk of HER hair takes care of that.
The guys are losing 1.5-2 lbs of weight per day. That's 4000-7000 calories per day, depending upon how much of it is fat and how much is muscle. Normal intake is less than 3000 calories, most of us gain wait on that much intake. So these guys are stressing/working pretty hard. From what I can see, the great majority of what they do is build pretty worthless shelters, instead of just moving around and finding shelter that nature always provides (usually within a day's hike) and forage for food as you go. I'd never trust roasting (on a rock, or speared with a stick) to get meat adequately "done". especially not turtles, fish, eggs, or sea food, and you lose nutrients with such cooking methods, too. Boil such food items, man, and drink the broth.
Only an idiot would drink untreated ground water. If they had known they were going to soggy-assed Borneo, and been not interested in drama, they'd have taken a double poncho and a water filter and just sat it out. The first ones, in Africa, went a week before they figured out that they should make sandals to protect them from thorns. I'd have done that first thing, using some bushy branches to brush the thorns out of my way, as i sought out fibers/bark to make into sandals. They took like 7 hours to move 5 miles, and he ruined his foot with an infection from a thorn, first thing. They also needed a means of carrying things, and a club and spear each. That all could have been dealty with in 4 hours, and then they could have walked the 5 miles in 2 hours, and still had time to make the fire at the waterhole. The guy who sunburned could have made a big "sombrero' or umbrella out of palm leaves. So far, only 1 of the guys and 2 of the women have amounted to a hoot.
The camera crews doubtless have guns and all the typical gear, so there's no real danger from the hyenas in Africa, nor the caiman-gators (unless walking in water over your legs) Snakes are pretty helpless critters, if you see them and dont step on them. I was surprised that they were able to catch that mongoose, and yes, they should have been setting traps. Especially for the lobsters, turtles, fish, birds and crawdads. They should have received some training in recognizing/using the local plants, too.