To get Milk in Cookie Clicker, you can complete achievements in the game. In doing so, you will be able to acquire milk at the rate of 4% per achievement. Also, whenever you unlock the achievements in order to get milk, you need to remember that you will only be able to do so by unlocking non-Shadow achievements.
The Milk n' Cookies is a craftable Clicker accessory that combines the effects of the Cookie and Glass of Milk.
Milk is a valuable resource which unlocks the Kitten series of upgrades that greatly increase cookie output rate in direct correlation to the amount of Milk the player has. Milk is gained by unlocking normal (non-Shadow) Achievements at a rate of 4% milk per Achievement.
An example of Toys floating on milk. Toys are interactive, physics-enabled objects that can appear in the left panel when Cookie Clicker loads. There are two types of Toys, one which takes on a textured image (similar in style to the Big Cookie), and one which takes on the image of a particular Cookie Upgrade.