<What's wrong with solar heaters?

Absolutely nothing, Tom.

It'll have to be either expensively indestructible, or cheaply disposible, though. And it would need to be small enough that every Joe could tote one around with little to no problem (preferably 'no problem'), or be large enough to be a crew-served kitchenette device (too cumbersome, I'm sure).

The MREs used a black pouch that you folded your meal into for about 30 minutes in the sun. Worked pretty good for heating chow in Panama (when it wasn't raining, that is), but not too well at Fort Carson, CO, in middle of January.

I'd say the easiest method is what I stated below.

Good food is important, but where "Uncle Sam wants macaroni and cheese that will remain tasty and nutritious for three years after it is cooked," I think the local GI would prefer a meal that has the ability to be immediate, as well as edible (i.e., at least tasty), whether it is hot, cold, dry, or wet.

Chow-chow,
Dan (I'm late for dinner!!)