Please share your experience in bringing expressed breast milk out for shopping etc. Do you store inside a cooler bag? How do you warm up the milk for baby?

I store them in a container then put in cooler bag.. I bring along a bottle of hot water.. when required to drink will just the hot water to warm up.. if in the restaurantu can ask them for hot water to warm up or if there is a nursing room will use the hot water to warm the milk up....