If you're packing to save weight, and don't have (as I do) serious cardiovascular issues, go for foods that are high in fats (although DO me smart and limit saturated and poly-unsaturated fats), such as tuna in oil, butter/margarine/mayo, and others. The reason is that fats contain 9 calories per gram, while carbs (including all sugars) and protein (you gotta have SOME but no more than 30-40 grams a day, which is like 1 oz of meat) only have 4 cal/gm. In other words, you get twice as much "food" per gram from fats. Yes, you need some balance (that's why you don't see a lot of people on the AT carrying ONLY tubs of Parkay!) but that's why a Snickers bar is actually pretty smart.
"Well a promise made, is a debt unpaid, and the Trail has its own stern code." -- Robert Service