I'd always assumed there was some numerological reasoning behind the numbers in Mark's stories of Jesus feeding the multitudes (6:30-44 and 8:1-10). A quick look through the New Oxford Annotated Bible answers some of my questions:

As he had fed the earlier crowd in the wilderness, implicitly composed of Jews, now Jesus also feeds the surrounding peoples in the wilderness. Seven is symbolic of the surrounding peoples, as twelve was of Israel. The two wilderness feedings echo thte two accounts of the giving of food to the Israelites in the wilderness.

I still wish I knew what the specific numbers of loaves of bread and fish meant—that's a question for later.