Growing up in Texas, we always had black-eyed peas with New Year's dinner - traditionally for good luck or prosperity in the new year. Invariably the story about Sherman's march was cited as the origin, but that explanation has always smelled like a "just-so story" to me. Wikipedia claims:

The first is associated with General William T. Sherman’s march of the Union Army to the sea, during which they pillaged the Confederates' food supplies. Stories say peas and salted pork were said to have been left untouched, because of the belief that they were animal food unfit for human consumption. Southerners considered themselves lucky to be left with some supplies to help them survive the winter, and black-eyed peas evolved into a representation of good luck. One challenge to this legend is that General Sherman brought backup supplies with him including three days of animal feed[6] and would have been unlikely to have left even animal feed untouched. In addition, the dates of the first average frost for Atlanta and Savannah, respectively, are November 13 and November 28.[7] As Sherman's march was from November 15 to December 21, 1864, it is improbable, although possible, that the Union Army would have come across standing fields of black eyed peas as relayed in most versions of the legend. In another Southern tradition, black-eyed peas was a symbol of emancipation for African-Americans who had previously been enslaved, and who after the Civil War were officially freed on New Years Day.[8][9] Other Southern American traditions point to Jews of Ashkenazi and Sephardic ancestry in Southern cities and plantations.[10]

Unfortunately, the sources linked in the Wikipedia article are ... less than illuminating, and my searches of r/AskHistorians turned up little. Do any of the experts here have some insights?