Don't worry too much about 'practicing' fasting, just deal with it. Have plenty of good light reading material, a movie to watch or something to keep your mind off it. If you're already PBing you shouldn't find it as bad as if you were still on the blood sugar rollercoaster.
I ate quite lightly the day before, can't recall exactly what - chicken I think. The worst thing I found was getting down that disgusting drink, and such a huge volume of it. There's different ones, the one I had was many liters and the effects took a while, while there's another one which isn't such a large volume and tends to do the job in a shorter time.
Really what you eat probably doesn't make a great deal of difference within reason. So long as you carefully follow the timings and instructions you are given.
It wasn't as bad as I thought it was gonna be. On the day, I told the doctor I was very scared (I'm a chicken!) and they kept me 'under' the whole time, one minute I was chatting to the nurse and next thing I knew I was waking up feeling fine. No ill effects at all though my guts felt a bit icky the next day.
So try not to worry too much.
If we’re not supposed to eat animals, how come they’re made out of meat? Tom Snyder