Fat is 9 calories per gram while carbs are only 4. I read a book about arctic sledding where they made their own "fat cakes" as provisions. They also didn't bring any other type of food apart from the cakes, because "without variation there is no disappointment".
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Steger and Schurke (and a few others) that took their dog sled teams to the N Pole carried a lot of butter for that same reason. If I recall (I read their book decades ago), Steger had a lot of intestinal distress from eating so much fat.
At home I average 30 to 35 percent of my calories from carbs, I have to eat a low carb diet to keep my blood sugar down. But on my recent backpacking trip I had an average of 49 percent of calories from carbs, most of those carbs were breakfast when I assumed that hours of carrying a heavy pack would burn off the carbs, and that assumption worked out well as blood sugar levels were good. I considered bringing a bottle of olive oil to add to my suppers to boost calories, but decided against it. I have done that on some other trips.
There are 7 calories per gram of ethanol, but I would not suggest relying on that source of energy for very much of the total energy needs.
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They had a no litter rule so they couldn't throw away their used tea bags. They found that the bags froze into ice cubes and added a lot of weight to their sleds, so they would dry their used tea bags inside their hats each night.
That is very impressive that they held to their rule. I would have been very tempted to tear open the bags and let the tea loose into the wind.