I think the cabbage "thing" comes from the Irish. Anyone know if that's true?
I have always heard that the black eye peas were symbols of coins and that you had to eat a "green" for the bills...therefore cabbage, mustard, collard, kale...as greens...generally any greens that will benefit with seasoning from salt pork or bacon...
The Irish side of my family always ate corn beef and cabbage on NY. The Austrian side always had pork and sauerkraut.
My father, who was never much for sentimental tradition, once told me it was because the only vegetable available in the winter was cabbage and an odd potato or two. :-)