Do you mean just to celebrate christmas or the reason for the season the birth of Jesus. I would say the same things they normally eat for celebrations all their favorite foods. Now if you mean for a buffet style dinner at the church/cathedral.lamb roast,ham,turkey veggies,fruits,loaves of bread(handmade), and traditional sweet treats(cookies).after the service/mass. According to what I read they may even fast that day til the big dinner is ready. Almost like thanksgiving.
