breast milk, unique constituents

Definitely a non-exhaustive list:

docsohexanoic acid	necessary for growth and development of the brain and retina, also for myelinization of nervous tissue
cholesterol	enhances myelinization of nervous tissue
taurine	important for bile acid function
choline	may enhance memory
enzymes such as lipases	important for digestion of fats
lactoferrin	binds iron and transports it efficiently into the baby; prevents iron from being used by gut bacteria
inositol	enhances synthesis of surfactant in immature lung tissue
poly- and oligo-saccharides	inhibit bacterial binding to intestinal surfaces
various proteins	bind calcium and zinc for absorption by the baby; supply amino acids to the baby
white blood cells	transmit maternal immunity to infant's immune system
nucleotides	building blocks of DNA, RNA, and energy storage compounds; enhance formation of immunity to infection
glutathione peroxidase, alkaline phosphatase, xanthine oxidase	important in prevention of infection
lactoferrin (above), lysozyme, secretory immunoglobulin A	line intestinal surface, prevent bacterial attachment and infection