I use either a screw top ziploc hard sided container with reflectix duct taped around it to insulate, or just pour the hot water in the freezer bag. Regular ziplocs are thinner and more likely to spring a leak at the seams. By the time the water goes in, it's no longer boiling and doesn't really do much other than make the bag hot to the touch (and rehydrate the food).
If you want an available source of bags that are in fact designed to handle boiling water you can either use foodsaver (vacuum sealer) bags, which are nylon lined with the same plastic as the ziplocs, or
get something like these.. I have cracked eggs into a foodsaver bag, sealed, and boiled it in my pot in camp the next day - perfect omelet as long as the bag does not touch the sides.