When slicing the Challah on Shabbos, after slicing a piece of Challah for himself, a man should cut another piece of Challah, an even larger piece, for his wife. In fact Poiskim say that according to Kabbalah, a husband should give his wife her piece of Challah before he gives a piece to anyone else at the table, even very Choshuve, honored guests. There are at least two reasons why the wifes slice is supposed to be bigger: 1) according to Kabbalah, and 2) as required in Shulchon Oruch to honor ones wife Yoiser MiGufoi, more than himself. In general on Shabbos, one is supposed to give a large slice to each person at the table so that it should be enough for the entire meal.