Well, survival rations, such as once by Datrex or other brands like Mayday and Survivor Industries, and army MREs are two different animals.
Basically emergency rations are composed of compressed, cooked wheat flour with oil.
Datrex brand, has coconut flakes, so it tastes like a coconut cake. IMHO it tastes pretty good for something designed to be eaten up to 5 years from manufacturing. Additionally, Datrex bars are subdivided into 200 calories chunks, and are sealed individually inside the 2400 or 3600 calorie overwrap. Pretty usefull if you are trying to ration your survival food, while at the same time keeping it from drying out too much.

Datrex Ingredients: Wheat flour, vegetable shortening, cane sugar, water, coconut,and salt.
Weight: 1.5lb (701g)/pack
Nutritional information:
Serving size: 1 bar, approximately 1.4 oz (42 g)
Servings per package: 18
Calories: 200
Carbohydrates: 27 g
Protein: 3 g
Total fat: 9 g
Sat fat: 2g
Mono–unsat: 6 g
Poly–unsat: 1 g
Sodium: 0.18%

Mayday bars to me tasted less moist then the Datrex once. Don't know if this is because of the extra soy powder they add to them, or the other ingredients, like vitamins etc. In a survival situation, vitamins are propably the least of your concerns. The bars tasted like a dry cinnamon cake. It felt like I needed more water to wash them down then the Datrex kind.

Mayday Ingredients: Enriched flour, vegetable shortening, sugar, corn syrup, soy flour, corn starch, potassium sorbate, vitamins (Vitamin A, iron, Vitamin E, riboflavin, Vitamin B6, Vitamin B12, pantothenic acid, copper, vitamin C, vitamin D, thiamine, niacin, folate, biotin, iodine, zinc), apple cinnamon flavoring.
Weight: 0.56lb (252g)/pack
Nutritional information:
Serving size: 1 bar, 1.5 oz (42.5 grams)
Servings per package: 6
Calories: 200
Carbohydrates: 27.5 g
Protein: 3.5 g
Total fat: 8.5 g
Sat fat: 1 g
Sodium: 1%

I haven't tasted the Survivor Industries (Mainstay) bars yet.