Breast Milk. It takes an extraordinary amount of effort to pump breast milk. It can be stored in a freezer for up to one year and is the best nutrition for a baby for the first year of life. Babies are often allergic to various types of formula, but it is extremely rare for one to be allergic to it's mother's milk. Mothers who produce a lot can feed babies who do not have access as well.
While we went out to dinner, my bitchy mother in law decided to the give the baby a bottle of formula because she doesn't agree with breatfeeding. So she dumped out the milk I left her! That stuff is liquid gold!!!
Prices shown in USD.