something that comes with something else, but is less important than it
sometimes in a specialized sense, including:
incidental expenses or when in context, just incidentals — minor expenses not budgeted or not specified
incidental music — music in a play, television program, radio program, video game or some other form not primarily musical. (The term is less frequently applied to film music, with such music being referred to instead as the film score or soundtrack.)
When speaking to Chichagov, Kutuzov incidentally mentioned that the vehicles packed with china that had been captured from him at Borisov had been recovered and would be restored to him.
Book Fifteen — 1812-13 (18% in)
There are no more uses of "incidental" in War and Peace.