Allegedly dates back to the Civil War. Those peas were originally used as food for livestock.
Then as a food staple for slaves.
So when Union Army General Sherman saw fields of black-eyed peas he ignored them because of their lowly state and razed/stole other crops. During the harsh winter Confederate Soldiers survived by eating the peas and in so doing turned them into a sign of luck and prosperity.
Some eat them with greens and cornbread. The peas represent coins. The greens represent paper money. The cornbread represents gold. Some eat cabbage instead of greens.
You must eat at least 365 peas on New Year's day to cover each day of the new year. Eaten with tomatoes it represents wealth and health.
I expect all southern rebs know that. I think it's superduper fascinating.