A gravy boat is a boat-shaped pitcher in which sauce or gravy is served. It is also called sauce boat, saucière.

susan I love gravy. :) It's one of my favourite foods.

Together I mean. Well, they are good separately but really good together

Gravy and mashed potatoes are delicious!

Thank you all very much for your points, especially dancingbear for his great explanation. Barry was the groom. I myself thought gravy boat maybe is kind of metaphor used there. So it is a sauce boat.