The phrase "winner winner chicken dinner" originates from 1970s casinos that were trying to attract players to underplayed tables. At the time, the most common casino bet was two dollars. Coincidentally, most casinos also offered a standard chicken dinner that was priced just under two dollars. "Winner winner chicken dinner" was called out by dealers when someone won at their tables, indicating that the player had just won the equivalent of a chicken dinner and attempting to attract others to come play at the table to have the chance to win the same thing.
Today, "winner winner chicken dinner" has become a playful exclamation used to celebrate a win while playing anything from board games to croquet to football.