sweeten the kitty

To raise the stakes, as in a game of poker, where the pot is called the kitty: “Before you decide which job offer to accept, perhaps we can offer you a few added fringe benefits to sweeten the kitty.”

Also, sweeten the pot or deal. Make something financially more attractive, as in I am unable to give you the new title but I could sweeten the kitty a little by giving you a raise. This idiom comes from card games such as poker, where it means “add money to the pool,” and uses sweeten in the sense of “make more agreeable.” [Slang; c. 1900]