The man who was being fitted for a custom-made suit is actor and director John Waters. While his character is not addressed by full name, it is clear from the mention of his first name and one of his films, that he's playing himself. It is the only instance, as of 2018, where a person who actually exists in the real world is portrayed on this show.
The movie viewed at the cinema is Frank Capra's It Happened One Night. One of the scenes shown is the famous hitchhiking scene with Claudette Colbert.
James Spader (Raymond Reddington) played Dr Daniel Jackson in the Stargate movie. Julian Sands (Sutton Ross) played The Doci, the Chief Prior of the Ori, in the the TV series Stargate: SG-1.
John Waters (John Waters) was in Seed of Chucky (2004) and Fiona Dourif (Lillian Roth) starred in Curse of Chucky (2013) and is also the real life daughter of Billy Dourif (the voice of Chucky).