Feeding breastmilk in a bottle

Gibbeanski
I haven't gotten to this point yet, but I've been thinking about how this is supposed to be done.
Scenario: you pumped breastmilk in a storage bottle and stuck in in the fridge. A couple of days later, you are going out in public and decide you want to feed baby with that bottle while you are out so you bring it with you.
1) Do you have to have an ice pack to keep it cool? If you do use an ice pack, how long is the bottle good for? What if you don't use an ice pack?
2) Do you need to warm it up before giving it to baby? If so, how (if you're out in public)?