Large platters are often called serving platters or trays.
The word for food and refreshments is catering or food service.
A person who serves food at an event is typically called a server, waitstaff, or waiter/waitress.
A person who is giving a party is often called a host or hostess.
A buffet typically allows guests to serve themselves from a variety of food options arranged on a table, while a plated buffet involves guests being served by servers from a pre-arranged selection of plated dishes.
Different types of buffet styles include traditional buffet, action station buffet, carving station buffet, and themed buffet.
To keep guests warm at an outdoor party, you can provide outdoor heaters, blankets, or hot drinks.
To keep hot food warm before serving, you can use chafing dishes, warming trays, or slow cookers.
A tray of appetizers is often called a charcuterie board, a cheese board, or a hors d’oeuvres platter.