The white Ferrari in which Peter Sellers pulled up at the fairground was his own. It's a Ferrari 250GTE, registration 5 XPC, one of several Ferraris owned by him. As at May 2017, it is now red and is in the U.S.
Scandinavian actor Tutte Lemkow played the German safecracker, "Siggy Schmultz". He appeared in many British movies and usually voiced himself (though many of his roles were non-speaking). Here, however, he was dubbed by Peter Sellers, which means that in Lemkow's scenes, Sellers can actually be heard conducting conversations with himself.
In the police station on "no crime" night, one of the cops can be seen reading a comic book based on the U.S. television show Car 54, Where Are You? (1961). Joe E. Ross and Fred Gwynne can be seen on the cover.
Michael Caine has a bit part as a gangster.