Warming bottles.

I thought about this earlier when I left the house and took my son with me. First time mom, I'm sure that's obvious. :) Anyway, how would I go about taking his milk with me? In a bottle, duh. But, I keep it in the fridge and warm it up before giving it to him at home. If I poor it in the bottle before I leave, should I warm it up first? Or just pack it and go. Should I carry it in a cooler? If so how would I go about warming it on the go? Or does it matter if it's warm?

The reason I'm asking like this is because he is on a 27 calorie milk. I have to mix it a certain way per hospital instructions. (he was a preemie) The way they have me do it is 13oz at a time. Which is great because I just pour it, warm it and feed him.

Sorry if this is a dumb question. I'm embarrassed to ask. That's why I'm annonymous.