I had my surgery last thursday and I wasn't given the milk diet as an option, however I did it for 2 weeks from choice after reading about it on here.
I had 3 pints of milk, 2 yoghurts (and used muller light yoghurts for choice of flavours etc) and NAS jelly. I often used the milk to make up the jelly as I couldn't get anywhere near 3 pints into me, and I had NAS crusha milkshake, NAS squash as well. Unlimited normal drinks and water.
I lost 17lbs on my preop before I had my surgery last thursday and Im now on liquids only for 2 weeks. I don't like greek yoghurt so just had the normal no fat ones, but check with your provider as to what you can have.
I could also have a stock cube, but these really turned my stomach so after 2, gave up with these.