When coffee ran short during Civil War days, a lot of folks including Billy Yank and Johnny Reb, fixed up this sort of drink
Coffee was made, especially by soldiers and hunters, by throwing a handful of whatever kind of grounds were available into the coffee pot with water and boiling. Egg shells were often tossed into the coffee to settle the grounds. Sometimes a bit of cold water was added to settle the grounds.
Dry brown bread crusts
Rye grain soaked in rum
Peas
1 handful small acorns, hulled, mixed with 1 handful cracked wheat
All these substitutes were roasted (only one type at a time) and then ground as coffee. They could also be mixed half-and-half with real coffee to extend it. Some believed it made "coffee" richer and clearer if a bit of butter or a whole egg (shell and all) was broken and dropped into the coffee substitute and stirred just before it was finished roasting and ground. Sweetening like honey was frequently added to make the brew more palatable.
At home, it was believed that if you had no cream to add to the coffee, it was an improvement to boil your milk and use it while still hot.