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']
(..) I mean, Mom's right about you. You have this part missing. Yeah, I said that first. Anyone whose protagonist makes a living selling old cap pistols and Joan Crawford cutout books... - Honestly... - Look, I'm not trying to be a martyr, but I think you'll be better off without me. (..)2011 Midnight in Paris