The main thing is to eat NO fats or oil the day of the flush, that includes butter on a potato, oil in the salad dressing, regular yogurt, eggs, etc. I haven't noticed any notable difference in the amount of 'stones' whethr I eat grains or fruits or veggies, but I do get less nausea and feel better the next day if I stick to mainly green vegetables.
My metabolism basically requires me to eat every 3 to 4 hours. I can't fast on flush day. The time I tried, I was ready to gnaw on the table legs by bedtime and it was the one time I wound up vomiting the oil mixture.
After trial and error, I've found that the best flush day diet for me is a either a banana or apple for breakfast, and two all veggie salads around lunch - one around 11:00 and another around 1:30/2:00. By bedtime, I'm a little hungry, but not starving and I don't seem to have too many of the side effects I normally get from not eating. However, I do drink a LOT more water during the afternoon, between 16 and 32 oz more than my usual daily intake, and that probably helps with keeping hunger at bay.
Also, for some reason, drinking the saltwater flush first thing seems to help me NOT be so hungry during the day (haven't figured that one out yet.)