My family also had Hoppin' John on New Year's but the side dish was always cornbread.
There were so many questions about its meaning that I googled and found this site--I have included a few excerpts which give a good idea of its origins and why it is considered lucky...
http://findarticles.com/p/articles/mi_qa3676/is_200501/ai_n9465890
The hearty combination first emerged on Lowcountry rice plantations. Abundant Carolina Gold rice and field peas re-created the rice-and-pigeon pea combination familiar to West African slaves, who were hungry for the comforting flavors of their homeland. Good food travels fast, and soon this stick-to-your-ribs specialty made its way out of the fields and into kitchens throughout the South.
One of the more popular theories suggests it's a Southernization of pois à pigeon (pwah ah pee-ZHAN), which is French for pigeon pea.
Tradition holds that when eaten on New Year's Day, Hoppin' John brings good luck. The rice signifies abundance for the coming year, while peas-specifically black-eyed peas-are thought to bring wealth in the form of coins. (Collard greens, a classic Hoppin' John partner, represent dollar bills. Pork also plays an important role in the dish, and it's for more than just flavor. Hogs can't look back, so pork represents the future.
(I never knew that hogs can't look back, hmmm).