Back in my carnivore days I liked the canned meat and sausage from the german rations - it is actually the same product you could buy from any german farmer who makes his own meat.
For the US MRE's I can say that you should go with the vegetarian ones - I liked most of them. This is my not so secret tip for anywhere where mass food is produced (MRE's, cantinas, hospitals). The veggie choice is often the better one, as they are made in smaller amounts - I won't say cooked with love

This applies not to the "apple slices" in the MRE's - which tastes like a truck full of chemicals hit an apple tree.
Oh yes, and avoid anything with egg in a MRE!