If you want to have milk on hand in case of an emergency, stock up on powdered milk and maintain a supply of bottled water with which to mix it. Shelf-stable milk must be refrigerated after opening and has a shelf-life of just a few months.
I would suggest bying cans of condensed milk instead of cartons. Cartons of milk go bad quickly while cans of condensed milk last for years. Then you can add water to the condensed milk whenever you wish to drink it.