The Longest Day but hard to say who was starring and who was a cameo and who was still an unknown like Sean Connery. Its poster does advertise 42 international stars.
How about Dave? Featuring cameos from both actors and politicians.
Do cameos by objects count? In The Longest Day, the shillelagh with which Kenneth More raps the APC is the one actually used on D-Day by the person he portrays. Similarly, Richard Todd could be counted a double cameo: not only was he actually there on D-Day - he helped capture Pegasus Bridge - but on camera he wore the very beret he wore that day.
A Guide for the Married Man(1967, Robert Morse, Walter Matthau, & Inger Stevens) had something like 30 “Technical Advisers”, being a group of then-prominent stars in short vignettes illustrating the techniques and pitfalls of adultery. Dated (and how!) but still pretty funny.
The 1933 Alice in Wonderland had a cast of cameos. Pretty much every single part was played by someone bankable. It didn’t have as many cameos (62) as The Player, but I don’t think it even had 62 roles altogether. For percentage of cameos to unknown actors, it would win, I think. The total number of bankable actors in small roles is more than 30 out of a cast of fewer than 50.
Also, one of the actors in AiW (1933) may hold the title for Most Cameo Appearances. Mae Marsh was one of the biggest names in the silent cinema. She had what we’d now call the “supporting actress” role in Birth of a Nation, and also was one of the stars of Intolerance. After Lillian Gish and Mary Pickford, she may have been the most popular actress of the silent era. She officially retired very shortly after the advent of sound, but actually, her appearances in films continued unbroken, she just went from starring roles to uncredited cameos, of which she made about 60. Add to that a number of very small parts where she is credited as “hysterical woman,” or “matron guarding prisoners,” plus a few TV appearances, and it’s well over 70, the last just three years before she died.
She retired from films because she wanted to raise her children, but probably also to avoid the studio system (a lot of silent stars retired for that reason), but I guess she still needed to bring in some money. She probably chose to be uncredited to stay out of the spotlight, and thus keep her family out of it.
How about voice cameos in live-action (as opposed to animated) films? E.g. a character on screen picks up the phone and it’s obviously Arnie as the on the other end.
Good addition and the poorly done sequel had even more. It had around 42.
Maybe around 15? Tough call between small roles and cameos in that one.
Good addition for a list. Reminds me of a TV movie version from the 80s that had a huge cast. 72 listed cast members or so. How many were cameos I am not sure.
Stretching the definition of “cameo,” though. Katarzyna Figura? Scott Shaw? Others who are known only as “That Guy” in Robert Altman movies? Cameos are supposed to be people we recognize, not just people working under their own names. It’s a game, but only the very best players will say, "That’s Joan Tewkesbury! She wrote Nashville and directed an episode of Felicity.