I didn't really think this post through, but I did buy some cravendale which is supposed to last three weeks.
It won't last three weeks. It's not even proper milk. It will probably last a week.
Cravendale is undrinkable anyway. A lot of supermarket milk isn't actually milk, but mechanically-super-compressed water with added whey and bacteria. You can't trust a thing they tell you on the bottles. Just buy milk that's come from an actual cow, not a laboratory.
Are cows just deconstructed beefburgers?