You would have been better off sticking the MRE heater in a bag of water, then pouring the water into the taters. You can get the water really hot that way. New MREs come with a water bag just for that. Not sure if a ziplock would melt or not, but I doubt it.
lol <img src="/ubbthreads/images/graemlins/doh.gif" alt="" /> I had the hot beverage bag too! See, this is why we all share ideas, you never know what you may learn.