Pour the milk, sugar, and vanilla extract into a pint-sized bag and seal. Fill a gallon-sized bag halfway with ice cubes and add the salt into this bag.
Put the milk bag inside of the gallon sized bag right on top of the ice. Seal up the gallon sized bag.
Shake the ice bag vigorously until the milk mixture inside of the pint sized bag freezes (about 5 minutes).
Take the milk bag out of the ice and throw away the ice bag. Pour the ice cream out into a bowl and eat.
