This feature/item is planned in a future version. It either does not exist yet, or does not yet have any known use.
A cookie is a non-perishable food item expected to be added in build 40.
A cookie can be eaten, providing the player with some positive effects, including reducing unhappiness.
Cookies can often be found in kitchen counters, bakeries, motel room fridges and candy stores.
From newitems.txt (Project Zomboid directory/media/scripts/)
Type = Food,
DisplayName = Cookie,
Icon = CookieChocolateChip,
Weight = 0.1,
HungerChange = -5,
UnhappyChange = -10,
Carbohydrates = 22,
Proteins = 1,
Lipids = 8,
Calories = 160,