To keep tortillas warm during a taco bar party, make sure you have some tortilla trays, which are short cylindrical containers with tops meant specifically for this purpose. If you warm the tortillas in the oven before the party, the tray will do a good job of keeping them warm and preventing them from drying out. To keep other ingredients warm, place them on an oven-safe tray and cover the tray with tin foil. The foil will insulate heat and you can stick the whole tray in the oven for a few minutes if it gets cold.