For a year, my daughter pumped over 100 gallons for a surrogate baby.
Here’s her review of some well-known breastmilk storage bags. While bags may change, this still gives you some basic tips of what to look for or what you do/don’t want when storing!
Post Edited to Add:
Honeysuckle bags were not available as of 2/24/2018, the company website is no longer responsive. Other bag companies have adopted their style, however.