Open your MRE package. Remove the entree pack to be heated.
Place packet under your clothing, against the skin of your torso. Keep in place for an hour or more. Body heat won't make the MRE hot, but it will keep it from being cold.
Put MRE near a heat source, if one is available, to make a heater that will make the MRE hot. Heat sources include an automobile engine, a rock that's been heated by a campfire or a radiator.
