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 in a cooler bag. I also bring a flask of warm water and a bowl to warm the milk up before feeding. if I'm goin to feed soon within the hr or next then I will just keep the freshly expressed milk in the bag for the next feeding. I always wonder how the other mummies bring expressed breast milk out too.