The USDA recently released a reminder of the importance of food safety during the holidays. Holiday parties, gatherings, and meals all offer opportunities for food to spend too long in the "temperature danger zone" of 40-140 degrees Fahrenheit.
There are three basic rules to follow to keep your holiday buffet safe: keep hot foods hot, cold foods cold, and avoid cross-contamination, especially between cooked and raw foods. Any perishable foods that don't follow the first two rules should be discarded after two hours. Replace or wash your serving trays between uses; it's better to have two or three small trays you can rotate out of the fridge or oven as needed than to have one large one that sits out for the entire event. Keep in mind that your serving utensils need to be attended to, as well: they should be replaced or washed often, or stored with the service end inside the food, and the handle well out of the food.
Cold food should be iced; you can create custom ice "dishes" by putting a ziploc bag into a container larger than your serving plate, (like a cake pan) filling it with water, resting the serving plate on top and freezing it all together so the ice molds to the bottom of your dish. You can hide the cake pan/ice pack with a pretty napkin when it's on your buffet.
Keep safe, happy and healthy this holiday season!