Pour these ingredients into a quart-sized zippered bag. This bag should seal tightly. Try to squeeze out all of the air as you seal the bag.
Put the quart-sized bag into a gallon-sized zippered bag, and fill the bigger bag up most of the way with crushed ice. Add 3 or 4 tablespoons of salt to the bag, squeeze out the air, and seal it up.
Smoosh the bags around for five to ten minutes. Shake them, squish them, and squeeze them around. Have fun, but be careful not to break the bags open.
After five to ten minutes, the ice cream should be sufficiently frozen to eat. We've added crushed up Oreo cookies, chocolate sauce, chocolate chips, and mashed bananas (all at different times - not together!) and have gotten good results.