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]
(..) No. Cool. You slaughter them. Nice. Potatoes. Grab it now. Meg's gravy is famous. It's practically a food group. Shower's free. I'm next. I want that. How can you watch this garbage? (..)1996 Twister