Go into a coffee shop and ask for some hot water from the coffee machine. If you stand the bottle of breastmilk in a cup/mug and pour hot/nearly boiling water around it it will heat up to body termp
Yes hot water is the way to go. I have a thermos especially made for this, I put boiling water in it before I go and it keeps it hot for hours and hours!
Re: Heating on the go