While I was shopping for food for my first bwca trip I found milk in a box! It's called Parmalat and you don't need to refridgerate it until it is open. It comes in 1 quart boxes so that shouldn't be a problem. We are bringing 2 quarts on our trip.

It may be a bit heavier to pack but it tastes just like real milk because it is. So I think it worth the extra weight. Besides... with me and my roomate the food pack should lose weight fast.