It is grated into boiling water, boiled for a bit, then milk is added. There is some dissension on the matter of boiling the milk. Some say it destroys the flavor, other claim it improves the flavor. Experiment to you own taste. Tea bags may be period, but don't look good.
Tea sets are available that contain a tea tin, grater, and compressed brick of tea.
They are inexpensive, and give a better look to the camp. To settle coffee ground or tea leaves, add a table spoon of cold water to the pot. Coffee is coffee. Often it was sold or issued green, to be roasted as need. Many coffee specialty stores can order green coffee if you want to carry it that far.