I think I remember that they had no firewood, so I assumed they were burning their clothing or catamaran material. The cactus could have been better utilized, but it may also have been a species that would have made them sick with diarea which would have killed them. They had no clear plastic sheeting, so all that salt water was useless in terms of solar still. They could boil the fresh water vapor out and soak it into a cloth lid, although I am not certain how well that would work. Discarding their water instead of tying it to the boat was perhaps their biggest mistake, other than not preparing for the climate and geography. But, then again, maybe they had everything they needed, only it was not on their person, so was lost in the storm. That episode shows the importance of a geography specific survival kit small enough to be kept attached to the life-vest or belt (preferably). Those guys survived out of sheer luck that someone happened to come by. One more day and they were dead.
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The Bell Curve says ignorance is normal.