A banquet is a long-time convention feature which has all but disappeared.
In the early days, a banquet was typically required by the hotel as part of the package — if you didn't agree to a banquet, you would be charged significantly higher rates or denied a package at all. A banquet was typically the culmination of a Worldcon, with a large fraction of the membership paying for the meal and attending. The banquet would include GoH speeches as well as the presentation of the Hugos. Normally, members of the convention who did not pay for the banquet would be allowed in for the speeches and Hugos.)
(At NYCon II, Dave Kyle was involved in what became known as the Mini-Exclusion Act as he prevented the Balcony Insurgents from coming into the banquet room after the meal to hear the speeches. "Dave Kyle Says You Can't Sit Here!")
During the 1950s and '60s it was common to have professional photographers take a group photograph of the entire banquet room.
Banquets at Worldcons faded away during the 1960s and '70s and by the 80s were uncommon.
Noreascon Three had a very successful 50th Anniversary Brunch banquet to celebrate the 50th anniversary of the 1939 Worldcon, and Bucconeer had a Crab Feast which also exposed to the world the danger of giving wooden mallets to 500 fans waiting to eat…
Convention banquets became less popular because of their logistics problems and because it became harder to get fans to buy tickets, which were frequently much more expensive than a better dinner elsewhere — hotel catering in the past was notoriously bad, the fare often the proverbial Rubber Chicken and Peas with "Bouncing Potatoes."
Regionals continue to have occasional banquets right up to today, sometimes because the hotels demanded them, sometimes (such as Midwestcon which only dropped the banquet in the early 2000s) because of long-standing tradition.