Breastmilk storage

Rachel • 24, Hull UK 🇬🇧 Expecting baby number 1, 👶👑 my little princess due 29th February
Not something if thought about but it seems I may have to start expressing so how long can I keep my breastmilk in: the freezer, fridge, and out (for outings etc, just in case!) 
I'm under the understanding when being kept in the fridge it should be stored at the back not in the door? 
Can I freeze bottles or die sit haveto be bags? Are they special Milk bags or could I use sandwich bags? 
And other advice appreciated
Thank you in advance