After a dinner like that you won't have to tell it. It'll just do it on it's own, I'm sure!
What's the most calorie dense food in the world?
Anything with the word "Armour" at the top of the label.
Remember though, there's a difference between useable calories and "empty" calories. Food is food in a bad enough situation, don't get me wrong. But some things will provide your body with more of what it needs and less of a high resulting in a crash.
I'd go for proteins, carbs and fats before I'd worry too much about calories: rice, peanut butter, meats (dehydrated, smoked or sausaged), cheeses, etc... Atleast that way you're giving your muscles what they need to survive. Calories are mainly just a way of gauging how much effort your body needs to exert to burn off the specific thing. Sometimes calories can be deceptive.
Be careful with how much fibrous stuff you eat, too. Granola might be a great trail snack (and it is! nom-nom-nom), but that's why nutritionists recommend a diet high in natural foods and fiber. Your body expends more energy processing it, so it burns more calories and uses up more of it stored fuel. So a great trailsnack doesn't always make a great "survival food".