I keep canned or evaporated milk on hand because a lot of casseroles call for it and I think it's better in mashed potatoes than sweet milk. Don't like the powdered stuff!
Milk doesn't like me (Lactoman will visit me) and the DH doesn't drink it, so what milk I use is mainly for cooking and baking. I buy the box milk and keep it in the pantry, because with bottled milk I would end up wasting too much.