The best way - by far - is to buy special breastmilk trays. They allow you to freeze ebm in 30 ML sticks.
Once they are frozen you pop them out and transfer to a double zipped freezer bag.
Many advantages :
> you will never waste ebm. It's impossible to know how much to freeze in one bottle as baby will change how much he drinks. So if you freeze 200 ML in one bottle but you only need 120 ML you will have wasted 80 ML. depending on your supply that can be heart breaking (ebm is gold!!)
> very easy to store and stack. You will be able to store heaps of then even in a small freezer
> cheap and easy as you buy normal freezer bags as opposed to overprice special ebm bags
> the sticks fit into a bottle. so when it's time to thaw just pick the number of stick you need and pop them into a bottle.
> if baby is still hungry for more after a bottle it's very easy to top him up without wasting ebm.
Seriously, this is the best option