You don't eat all the ice cream in one sitting. If this random ice cream[1] is an indication, serving size is half a cup, so a half gallon should provide 16 servings. If you like the flavor, why not buy 16 servings at a time; if you live in a household with four people, that's 4 sittings of ice cream.

[1] https://www.target.com/p/breyers-original-ice-cream-natural-...