I don’t think you need to stock up on anything. The only thing I consume during my extended fasts is black coffee, tea, and some sea salt that I dissolve in water.
I think there may be things “allowable” on a water fast to some, like bone broth or some fat, but for me I find it unnecessary and I actually think it makes it harder for me. Your mileage may vary.
If I was at a good level of Ketosis before starting my fast I never really get hungry outside of the psychological desire to eat at certain times, it isn’t true hunger. But when I consume bone broth during a fast my hunger skyrockets, and I start really wanting food. It is like that little bit of nutrient primes the pump for my body to expect more.
I think the same thing applies to non-caloric sweetened drinks. It may not have calories but I think it has physiological and psychological impacts that are counter to our goals during a fast.
So my advice would be to make sure you are having good Keto meals before starting the fast. Keep consumption during the fast simple: water, black coffee, unsweetened green or black tea.
Lastly ease out of the fast if you go more than two or three days. I have bone broth to break the fast and then ease in to a moderate sized keto meal a few hours later. I have heard that a high carb meal immediately following a fast could cause potassium imbalances, but I don’t have a source for that information at my disposal right now.
