The car was filthy when he returned it to me, and 'to cap it off' [='to top it off'], there was almost no fuel left in the tank.
a 'shower/bathing cap' [=a head covering that people wear to keep their hair dry when they are showering/swimming]
They may not like being called careless, but 'if the cap fits, wear it'. [=('US') 'if the shoe fits, wear it']
(..) in a Pan Am uniform sitting in a white Coupe DeVille out in front of Terminal J. That's the charter terminal. Can you get a look at his face? He's got his pilot's cap on. Carl, I think it's him! ? ...Just say the words, and we'll beat the birds ? ? Down to Acapulco Bay... ? (siren blaring) (..)2002 Catch Me If You Can