According to this website, the phrase originated from Las Vegas. It says that years ago every casino in Las Vegas had a 3 piece chicken dinner with veg and potato for $1.79, and a standard bet back then was $2. Hence if one won a bet, there would be enough for a chicken dinner. Anyway, thats just hearsay, don't know if there is any truth in it.
21 follows 5 students and their professor as they took Vegas casinos for millions in winnings. Of the 5, the most talented student, often termed "boy genius" Ben Campbell (Jim Sturgess) realises that he has a head for cards counting and subsequently leads the others during their Vegas casino visits. He finds out about the possibilities he could have with all his winnings, and also the dangers that accompany it. As he struggles to juggle his ordinary life as a student and in Vegas where he can be anyone he wants to be, he sees the people whom he can truly trust and depend on. Ultimately, he has to decide between his friends, the money and his lifestyle.
The movie was inspirational, really. From the bling and the extravagant lives our high-rolling gamblers led, the show also had an inspirational story line behind it - especially more so that it is based on a true story. It is a very enriching movie, though the directing and writing isn't nearly as impressive and plot was rather clichÃ©.