You will need pint ziplock freezer bags, gallon ziplock freezer bags, whole milk, sugar, vanilla, rock salt (or kosher or canning salt), lots of ice, bath towels, and a friend.
In each pint bag, mix 1 cup whole milk, 2 Tablespoons sugar, and 1/4 teaspoon vanilla extract. I found it easier to put the sugar and vanilla in the bag first, then pour in the milk and zip closed, removing air as you tightly seal the bag. This will make one bag of home-made ice cream.
To make the ice cream, fill a gallon ziplock freezer bag 1/2 full of ice. Sprinkle on 1/4 cup rock salt. Place one or two bags of milk mixture inside, then fill bag with ice and sprinkle on another 1/4 cup of rock salt. Seal bag tightly. Cover with a bath towel, making sure to keep the top of the sealed bag upright. Then...shake vigorously and continually for 5-10 minutes. Choose a partner to help with the shaking, being CAREFUL not to DROP IT!! Ice cream is "done" when the milk bags feel firm when squeezed. Remove ice cream bags from larger bag of ice & water. Wipe the outsides of the ice cream bags to remove any salt residue. You can eat right from the bag or can pour it into a bowl.
The salt makes the ice colder as it causes it to melt. The towel helps keep your hands from freezing as you shake the bag. If you used rock salt, DO NOT POUR the ice & water DOWN THE DRAIN!!! The rocks leftover from the dissolved salt will CLOG the drain! Empty the ice & salt water mix onto a gravel driveway or in a street gutter. DO NOT POUR ON CONCRETE SIDEWALKS OR GRASS!!! The salt will DAMAGE the surface of the concrete and will KILL grass!!!