Do you think it helps to eat a lot the last meal before 3 day fast?
Or just go for it?
I just did 68 hrs before the holiday. Ready for another 72.
Help what? What are you wanting to accomplish or avoid with your prep?
Example, if it’s for something like staving off hunger pangs, it won’t help much beyond the first few hours. Lower carb, higher fat (& a bit of fiber if you prefer) tend to help with hunger, in my experience.
For shorter fast of only a few days you don’t need to do significant prep unless you prefer to.