Büsching says: Early in the morning he first drank a few glasses of water, into which a little distilled fennel water was poured in the later years of life, and afterwards 2 or 3 small cups of coffee, with and without milk. As a means of preservation against a stroke, he had a spoonful of white mustard put in his coffee.

While looking for that, I also saw that he has a date for the "days without sleep anecdote", saying that Fritz used to tell the story in his old age: 1734, while he was on campaign at the Rhine, "he tried, together with a couple of other young people, not to sleep at all, but be busy all the time, in order to live double the time as other people did, so to speak. With the help of large amounts of coffee, he made it to four days and then had to stop because he fell asleep at the table and his blood was running too hot."