Mainstay.

I hate coconut, and most ER have a coconut flavoring. Mainstay tastes like a cheap lemon cake...which is completely acceptable.

I buy the 3600 calorie Mainstay, because it's broken into 9 squares. Each square has 400 calories ... Meaning you can eat one square for breakfast, lunch and dinner and satisfy the minimum safe caloric intake for a day (1200). Obviously you'll like be burning through 3x this amount in a survival situation, but at least you'll prevent systemic problems by consuming a min.

Keep freezer quality ziplock bags with your ERs. This allows safe storage after the foil has been broken. Think about losing 3 days worth of food because you slipped into a contaminated stream!