The Earth beverage on which Captain Kathryn Janeway famously depended, rationed aboard Voyager and the cause of at least one detour into a nebula.
Coffee is drunk throughout Star Trek, but it is associated above all with Janeway, who takes it black and regards it as essential to command. With replicator energy rationed in the Delta Quadrant, keeping her supplied becomes a running concern, and Neelix's attempts at a local substitute are not well received.
In the early Voyager episode The Cloud, a shortage of power for the replicators prompts Janeway to order the ship into a nebula in search of fuel, with the remark that there is coffee in it. The nebula turns out to be a living creature.
The habit recurs for the rest of the series, including a memorable demand for coffee before facing the day in Bride of Chaotica!, and it is carried over to her later appearances in Star Trek: Prodigy.