In an outdoor restaurant scene, one of the people sitting in the background is the father of the director Todd Haynes. His sister Wendy is also in that scene.
Many interiors such as Carol's house were filmed in Todd Haynes' family and relatives' houses. The exterior of the St. Tropez restaurant (the next scene after the dinner where Carol doesn't laugh at the vibrator joke) was shot, remarkably, using the exterior of Haynes' parents house. The street that opens the film is also the street where their house is located and his mother's car can be seen in the shot.
In the shot of the White family photos, real pictures of Julianne Moore from childhood and high school were used.