We tried this a few years ago while on a multi day peak hike/summit. The bags do not hold up vey well to the hot water or heat and we had more them one bag that lost any sense of plasticity, if you will. Keep this in mind when you are cooking over your "go big or go home" fires...

Now days, we carry the food in the bags and heat water in the pot shown below then put the food in (without the bag). This pot is made from hard-anodized aluminum with a titanium coating. It holds just under a liter of water and the rubber coated handles are much better then uncoated style. These pots are $28.00 at MEC and well worth the price.



As for the leaching, thats a good question. most commercial freeze dried bags are meant to be heated with hot water. The vac seal bags are not much more then gloried ziplock type plastic and you should contact the manufacturer of the bags you use and ask them.