I always refer back to "the book" and it says you don't need to take any supplements on this fast, as all your nutrients are covered in the lemon/syrup/pepper. However, I have an irregular heart beat and take prescription meds along with a dose of potassium. I must do this for my health - as if my potassium drops to low, or I get into an irregular rhythm, then I end up in the ER.
In the end, do what you feel is best supplement wise. But I would definitely forego anything that contained sugar.