I am Italian, so I beg your pardon if I have badly submit the question. Perhaps this forum is'nt the right one. I know what kitchen-sink means literally. So, why in english is used this expression also for "neorealism" ?
A game in which at least one of the player sacrifices most of his pieces, even the kitchen-sink, in an attempt, possibly in vain, to win the game.
If you have a long list of items and you add to the list even the kitchen-sink, then it means you have included just about everything.
Whether or not the game in question was such a game, is another question.....
Since ctrav mentions neorealism, I would say that the "kitchen sink" can stand for two ideas:
1) as others have said, it can mean that which might be taken on a journey, but which is cumbersome and inessential;
2) in art and literature, and particularly plays and film, it can refer to representations of the working classes and their humble difficulties. http://en.wikipedia.org/wiki/Kitchen_sink_drama