how to take breastmilk on outing?

Sh

if I go out how do I store and feed a bottle of breastmilk if I'm gone let's say 4 hours? do I take bottle from fridge and just store in insulated portion of diaper bag? do I put it with ice packs? when it's time to feed how do I warm it? do I warm it..? or should I just take it out and let it get room temp if it's on ice packs? ugh I'm so confused