Luckily, some of the MREs are changing - i.e. Tuna.
However, most are chock full of sugary snacks (the result of polling the military of what they want in a meal, not what they need).
I say it depends on your output and what the "field" means to you. But Whole Foods has almond butter in single packs that is awesome and calorie dense. Its less sugar than traditional peanut butter. You can supplement the jerky with dried fruits (esp the ones without sugar added) to get the protein/carbs balance.
If you are doing high output work (humps, etc) vice driving around in a vic, I'd keep eating the entrees but chuck out the deserts. Better, trade the deserts to that tubby next to you for another entree.