Hey Man You See That Guy Over There - How does a bag of milk even work without spilling everywhere?

Why not just have it come in its own cohesive container (such as a carton) and avoid needing the bag at all? This is the question my eagle blood demands an answer to.

Never in all my years living in this great northern land have I ever seen bagged milk. I'm pretty sure it's all an elaborate ruse perpetrated by the Americans to steal our last remaining pennies.