How to store breast milk. I prefer Lansinoh bags. Fill with milk (I typically freeze in bottle size portions - 4oz) fill, slowly close, pushing out any big air bubbles, and freeze laying down on a flat surface (use a small cutting board if needed). Then easily store frozen bags library-card style using the FIFO method (first in, first out). So easy to grab what you need for the baby's next bottle or daycare.