You’ve done it before, so you know what to expect.
I realized that on the no food day it was okay to have beverages that I otherwise avoid like regular apple juice and my favorite Korean sports drink, Pocari Sweat*. I also had low carb options like coconut water and tea. In fact, that was a bit of info I gleaned from this thread because @Cinderfella mentioned using white grape juice on that day.
Good luck! This forum and others are great for sharing and getting info.
*Something that my Seoul-based endo nurse recommended to me when I lived in South Korea. I managed to get food poisoning of some sort, had taken insulin, but couldn’t keep food down.