If it's true that all good things come in threes, then matzo fits the bill. The crisp, flat bread made from plain white flour and water is served in a stack of three either on the Seder plate or next to it. It's a modern-day version of the unleavened bread eaten by the Jews when they left Egypt in a hurry with no time for the dough to rise. And the number three? That's said to represent the different castes of Jews.