I used to breastfeed from a bottle . I would store in the refrigerator . If it was frozen or cold from the refrigerator I would thaw it out by sticking it in a cup of hot water .

Like taking frozen breast milk with you..? I'm not sure about that. I stored my breast milk in the refrigerator and when it came time to leave I put it in an insulated bag right before we left. Then I took it out to warm up to room temperature about an hour before my baby had to eat.