My suggestion would be a 'remote' gas can type of stove. to many to choose a best one. You can even get 'knock off' ones on ebay at silly prices, I've used them and found as good as 'brand' named ones.
I'd get a wide 1.5l pot with a lid, should be able to fit two BITB meals in that, plus as long as labels, etc don't come off, can use water for something else, making a drink,(coffee,tea), of a cup a soup, etc.
If the labels come off, or packet stains water, you can always put into a bottle and use as a hot water bottle in your sleeping bag. Dump out in morning and fill with fresh water.