Lentils are the traditional Italian New Year's Eve food associated with prosperity because of their coin-like shape.
In Italy, lentils are commonly served around New Year's Eve, often alongside cotechino or zampone, two pork products associated with abundance and good fortune. Their small, round appearance is compared with coins, so eating them is thought to encourage financial prosperity in the coming year.
Cotechino is a seasoned pork sausage, while zampone is a stuffed pig's trotter. The combination of rich pork and lentils is especially associated with the Italian holiday meal and is served in many regions.
Customs differ among Italian families and regions, so lentils are not the only New Year's food eaten in Italy. The prosperity symbolism, however, is the key reason they are repeatedly linked with the celebration.