Pumping mommas please read!

Hi! I have been pumping for 6 months and am wanting to stop and use my freezer stash. this may be a stupid question but what do you mommas do when you are out and about and need to feed your babe. Like if you are going to be out for the day or something and need to feed your babe, and you thawed your frozen milk in the fridge over night but how do you like transport it or warm it up? Do you give it to them cold? Do you just use formula when you are out? Please let me know :)