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This was an easy one.
All of our sources essentially agree that the origin of the phrase stems from one of the original loss-leader meal deals: a three-piece chicken dinner with potato and veggie that cost $1.59-$1.99.
Meanwhile, a standard table-game bet in those days was $2.
So when you won your $2 bet, you'd earned the equivalent of the chicken dinner (with a little change thrown in).
Today, to show how things have changed since then, after winning a $50 bet, you might say something like, "I had a hunch and won a Bacchanal Buffet brunch!"