Pour milk from bag into glass.
Empty last bit of milk out. Waste not, want not, that's what I say. (Look, I'm sucking milk out of a milk bag!! Hee hee.)
Get new bags from fridge.
Put new bag into milk bag container.
Cut corner off bag for ease of pouring. If necessary, bite corner of bag. (The cat is optional)
Throw out little piece of plastic and you're done!!
Let the cat drink the milk, as you just wanted to take some pictures of it.
I hope this clears up the whole "milk bags" issue. If there are any questions feel free to ask, but there's really not much more to tell.