Cynthia's plane is a Lockheed Vega 5, the same type as was owned and flown by Amelia Earhart.
Katharine Hepburn's second film and the first where she receives top billing.
Finds for the opening "treasure hunt" scene include a life-buoy from the S.S. Venture, which was the ship featured in King Kong und die weiße Frau (1933). That movie was being made on the same lot at the same time, with Selznick also as producer.
According to Jay Leno in Jay Leno's Bugatti and Maserati (2018), the Bugatti Type 38A American Roadster used in this film was owned at that time by Charles Howard, the owner of Seabiscuit, and is the only American-bodied Bugatti ever made. Howard ordered the chassis from Bugatti and had it sent directly to coach builder Walter M. Murphy Company of Pasadena, California who built the body for it. The trunk was replaced by a rumble seat to accommodate a movie camera for this picture. Because of its rarity and provenance, this car would probably go for at least $1M at auction in 2024.
When this movie was made, Colin Clive was 33; Billie Burke, who played his wife, was 49; and Helen Chandler, who played their daughter, was 27.