As I discussed in an earlier post on what medieval people ate, for most of the population, including the aristocracy, food choices were very limited by our standards and very bland. But for a feast, to celebrate a great holiday (like Christmas) or a special event (like a wedding or knighting), cooks at an aristocratic household would throw themselves into creating something special.
Because the daily norm was to have just enough food to get by (dieting was not a big concern in the Middle Ages), one mark of a feast was for everyone to have seconds. Another marker of a feast would be to have a great many courses. A feast would start in mid-afternoon and go on until no one could eat any more.
A good feast would include soup, several different kinds of meat (fish, fowl, red meat), plus vegetables, cheese, and puddings, as well as plenty of bread, of course. Spices were used enthusiastically. Some birds which we would not think of eating, like swans, would be roasted whole. (They didn't have turkeys, though they did have geese; maybe they were making do with what they had.)
It was considered extremely elegant to present the bird looking as though it still had feathers. Bits of vegetable curls (shavings of turnip, say) could be stuck onto the roast carcass with honey. Something similar could be done with a pig, which might be presented whole, an apple in its mouth. Food was supposed to look visually special, as well as tasting special.
Because a feast was a display of wealth and elegance as well as a celebration, a great deal of attention went into the setting. Special wall hangings would be brought out. Medieval castles did not have dining rooms, so trestle tables were set up in the great hall for a feast, with table cloths for all--or at least for the most esteemed guests. Everyone was expected to wash their hands, and servants brought basins and fine towels.
Seating was strictly hierarchical, with the most esteemed guests at the head table with their own chairs, lower status people at long tables with benches along the sides, and others somewhere in between. Guests were expected to wear their finest clothes. Everyone got plenty to eat, even though the high table would have elegant table ware, while those down on the benches would be happy with a thick slice of bread on which the meat was piled. They had spoons but not forks, requiring eating with one's fingers--part of the reason you washed carefully before dinner.
Because no one can eat without stopping for six hours straight, there would be interludes of entertainment. Music, song, and humorous skits filled the gaps between courses. In the King Arthur stories, the king would refuse to eat on a feast day until some marvel had appeared--which of course always happened in the stories Because the wine flowed freely at a feast, there was doubtless a great deal of joking and laughing as the evening wore on, whether anything was funny or not.