On the same day as the funeral scene was filmed, President John F. Kennedy (a personal friend of Frank Sinatra's) was assassinated.
When Alan Dale (Bing Crosby) is invited to take a seat when first introduced to Robbo (Frank Sinatra), one of the hoods says, "Take a seat, Pops." That hood is played by Crosby's son, Phillip Crosby. Bing gives him a sidewise look.
The two lesser-known Rat Packers, Joey Bishop and Peter Lawford, don't appear in this film. They were essentially "replaced" by Peter Falk and Bing Crosby, respectively.
Making this film should have been fun. Instead, by more than one account, it was a waking nightmare for all involved. John F. Kennedy was assassinated soon after filming started, casting a pall over the entire set. Not long after that, Frank Sinatra Jr. was kidnapped from his dressing room at Lake Tahoe, Nevada. (Upon payment of a large ransom, he was released, unharmed, a few days later.) Victor Buono (Deputy Sheriff Alvin Potts) later observed that it was a minor miracle that filming was completed at all.