A lot depends on the hospital. I was done at Bournemouth and did a 2week pre-op milk diet. This is designed to shrink the liver by forcing it to use its sugar stores & therefore make it easier for the keyhole survey. I lost a stone on 2pints of milk, 2low fat yoghurts & a sugar free jelly a day. I had the option of bovril or bouillon. Plus of course tea & coffee as I wanted. I also tended to chew a sugar free gum stick as the milk tendered to leave a strange taste in my mouth, spitting it out once the flavour or taste had gone whichever was sooner. I split the milk into half pint drinks for breakfast, lunch, tea & supper adding the yoghurt & jelly as snacks between at break, lunch & either when I got home or for supper, as I felt the need.
For the first couple of days it was tough & I felt very tired napping when I got home at 4pm. After that I woke on about the 4th day feeling great & raring to go as if something had clicked in my brain & all was fine.