if you’re trying to lose weight eat less than normal or what you want normal to be from now on. When you fast is like a ‘reset’ and you can redefine what your body expects, and you can eat much lower amounts and your body will accept this is the new settings.
If you addicted to fat and sugar junk food then the desire for that will have disappeared, so don’t eat them.
If you don’t care or are fasting for some other reason like resilience or religion then do what you like. You can go crazy if you wished. But the big point is if you eat and drink very small amounts gradually then your body has to choose what the new food and drink gets given to, so it becomes more efficient, and if you changed your calorie number and type of food significantly then it would be easy to adapt to.
I feel like I have seen in a few places that it’s when you get to fasts over 3 days that you really need to introduce foods slowly - start with liquids and broths for 1/3 of the time you fasted before introducing solid foods and then only small meals.
Under 3 days I wouldn’t eat too much at once right away but wouldn’t be as harmful.