Amid scenes of pomp and pageantry, Charles and his wife Camilla were crowned at London's Westminster Abbey on Saturday in Britain's biggest ceremonial event for 70 years.
Charles and Camilla have not been seen since they appeared to cheering crowds on the balcony of Buckingham Palace following the coronation, but senior members of the family were expected to be out in force on Sunday.
The king's younger brother Prince Edward, his sister Princess Anne and Princess Beatrice and Princess Eugenie, the daughter of Prince Andrew, were due to attend "Big Lunch" events, joining some of the estimated 50,000 street parties being held around the country.
Prime Minister Rishi Sunak will be among those hosting a coronation lunch, with the guests including Ukrainian families and youth groups.
"Come rain or shine, thousands of friends and neighbours are coming together this weekend to put up the bunting, pour the tea and cut the cake at street parties and community events across the UK," he said in a statement.
Later, Charles and Camilla and other senior royals will join an audience of 20,000 members of the public and invited guests for the Coronation Concert at Windsor, the king's palace to the west of London.
Among those performing will be Take That, Nigerian singer-songwriter Tiwa Savage and pianist Lang Lang, while Hollywood actor Tom Cruise, British actor Joan Collins and Winnie the Pooh will also feature.
The event will also include a Lighting up the Nation with projections and laser displays illuminating landmarks and areas of natural beauty across the country.
However, not everyone has celebrated the coronation, with anti-monarchists angered after being detained for hours on Saturday for planning to protest.
Police said they believed the protesters planned to disrupt the royal procession.
Amid questions over whether the police response had disproportionately curtailed the right to free speech, Culture Minister Lucy Frazer said that she believed the police had overall "managed to get that balance right".
