The bonus he received in addition to his salary was pure 'gravy'.
They're trying to get on board the 'gravy train'.
a 'gravy' boat [=a container for serving gravy]
(..) is not easy. I mean, some people settle for plain old beef kidneys. Got no right to cook anything, them. Oh, and the gravy. Don't get me started on the gravy. You cannot give up on the gravy. No gravy, no pie. (..)2014 TvShow: Game of Thrones Title: Mockingbird Season: 4 Episode 7