I was exaggerating a bit when I said a day or two. I guess the main thing the milk is missing which is important not to go long without is vitamin c and niacin,since the body can't store much of those. If you drink a gallon a day of milk you would be getting enough magnesium and sodium, however I still say the saturated fat is a concern. Of course you could drink skim milk rather than whole milk, but then a gallon of milk wouldn't have enough calories. Perhaps there might also be some concern about excess calcium intake, although that would be a long term concern, not a short term one. A week at a time just drinking milk might not be so bad though, especially if you take b vitamins and vitamin c with it. A month or more might start to be a big concern though.