Opening the main pocket will not change the shelf life and it makes it easier to store. I had three of them in my pack this weekend and taking them out of the main pouch made it so much easier for packing. BTW beef and mushroom is lip smacking good. But what I really miss from that is tobasco sauce. Somehow all the new MREs are missing it.

Storage time is about 5 years but this can be affected by temperature. I keep two rations in my car and than rotate them when I go kayaking or camping.

Tip:
If you don't want to use heaters or stove to warm them up, take the main course out and place it against dark surface in the sun 1 hour before eating. With crackers it's as good as cooked.

Matt