ideal survival foods do not make you thirsty after eating them. This is one reason why boat rations are popular.

ideal survival foods also provide a wide range of nutrients. You need potassium, magnesium, salt, vitamins, etc. - another reason why boat rations are popular. Whatever food you pick needs to be somewhat complete.

I don't eat fruitcake. I fall into the "hate-it" camp, so I can't say whether it makes you thirsty or not - maybe someone else can comment further.