Honestly MRE's suck ass unless your really, really, really starving. One (1) Military MRE has enough cal's to sustain a Soldier/Marine, ect for a 24 hour period, as long a you have enough water to go with it, or you will dehydrate yourself.
If you need emergency food, I would say throw a few cans of chef boyrdee in your car and call it a day. Better tasting and easier to poop.