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]
(..) - Hi. or are we waiting for four wet bridesmaids? Oh God... well, it started about a half hour before the wedding. I was in the room where we were keeping all the presents, and I was looking at this gravy boat. This really gorgeous Lamauge gravy boat. When all of a sudden- Sweet 'n' Lo?- I realized that I was more turned on by this gravy boat than by Barry! And then I got really freaked out, and that's when it hit me: how much Barry looks like Mr. Potato Head. Y'know, I mean, I always knew looked familiar, but... Anyway, I just had to get out of there, and I started wondering (..)1994 TvShow: Friends Title: The One Where Monica Gets a Roommate Season: 1 Episode 1