Many moons ago I worked at an espresso bar and they used to have the 5gal bags of milk with what looked like a baby bottle nipple on one end. You'd put the entire bag in this... well I guess it was like a refrigerator that sat on the counter, and the plastic "nipple" part would face downward. Then at the bottom it had a handle so you could just press that down and milk would pour into the cup underneath.
I think I'm making this sound a heck of a lot more complicated than it really was, but it's one of those things you'd have to see to really get
I tried to find a picture of it, but I haven't found one yet.
But yeah, so we do have bagged milk here, but it's probably not something you see on a regular basis unless you work in an espresso bar with one of these machines