The typical way is some sort of homemade bone broth, since store-bought broth is usually just colored water.

Some people will use zero calorie sports nutrition drinks or some kind of magnesium and/or sodium pill (since it's not just NaCl you're losing when fasting).

I added a quarter of a teaspoon of salt to water everyday, and took some magnesium pills every few days. Did not supplement potassium, though common sense says I should have.