A cookie is a treat that can be fed to a puffle or a penguin. Each color of puffle has its own unique way of eating a cookie (for example, the Red Puffle throws it like a frisbee, catches it, then eats it).
A box of 20 cookies can be bought for 100 coins. When puffles still had a player card, a cookie could be bought for 5 coins to feed a puffle. Cookies lower the Puffle's hunger, rest, cleaning and need to play.