I remember those plastic bags of milk. Must've been a Canadian thing - we never saw them here. Not sure what the reasoning was. Maybe it made shipping larger quantities easier/cheaper? I know, back then at least, they were used with dedicated reusable "holders". Lot easier to handle, because you got a handle out of the deal, while our glass jugs or paper cartons were a little unwieldy - especially for kids or anyone with small hands or low strength. When blowmolded plastic got cheap and easy, nearly all containers had built-in handles. Of course, that was long ago. Hell, it was still not unusual to get daily milk delivery in glass jugs.