My letter didn't say anything about food.
Recommends a pint of water an hour before.
My bladder wasn't quite full enough on my first. I think that was linked with my scan being in the morning when I'm usually less hydrated. I'm going to drink a little more this time.
Obviously wear something you can comfortably access your belly and your arm. You might have to wriggle trousers /knickers down a little, you're not exposed at all, it's just to move the waistband out of the way.
It might be worth taking a little cash in case you have to pay for pics.