I was wondering what that reference to a chemical heater was. I know they didn't have them for C-Rations and there was not heat for MREs when I was in the army. But that was 1986-90 so I guess they've evolved some since then. I got to try more than enough of the first couple of generations of MRE. The second generation made some nice improvements- that's when they started including the little Tabasco bottles, around 1988. They also added M&Ms to some of them, and this odd little oat-bar that had a consistency/texture like a block of compressed sawdust but had a truly AWESOMELY delicious taste!
I also remember learning some things about cooking MREs. The early ones had some dehydrated items, the hash-brown-type potato thingee in one meal and a pork patty in another. They could be eaten dry, but could also be reconstituted and even grilled once water was added. I also learned that if one combined the sugar with the contents of the creamer packet then heated the mixture in a spoon over a couple of matches, the result would be a sort of pseudo-cookie. I also really liked those dense baked-in-the-foil-pouch cakes in the MREs and figured out how to make icing for them with the sugar, creamer and the instant cocoa, all mixed together with just enough water to make a spreadable consistency.
My best MRE experience was during a training excercise in the Mojave desert. I was detailed to a live-fire support detachment so I wasn't in the wargames. The detachment was SO relaxed and laid-back! I worked without supervision (I hope the statute of limitation has run out on that...) and was told that MREs could be had from a cargo trailer over on the edge of our area. I took a case every few days and just ate the parts I liked and plenty of them!