Currently reading this history of the music hall, the British counterpart of vaudeville and precursor to variety. My favourite RPGs tend to be things like "Call of Cthulhu" and "Forgotten Futures" with a strong Victorian to Georgian (George V, that is) tone and history, but I often feel that the popular culture of the time is ignored when it should be a vital part of the world and the characters. NPCs ought to be playing records, going to the pictures, whistling the latest hits, referencing movie stars and stage actors, encouraging the PCs to read a new novel they're enamoured with—or recommending they avoid one they dislike.
A few sentences here and there, a name dropped, an encounter when shopping for sheet music or looking at the posters advertising coming acts… it doesn't take much to add to a great deal of flavour to the world and make it feel alive, rather than like those cheap cartoons where the only people moving or even present in a scene are the PCS.