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']
(..) My dear good friends! How dost thou Guildenstern? Oh Rosencrantz, good lads, how do you both? - As the indifferent children of the earth - Happy in that we are not over-happy On fortune's cap we are not the very button - Nor the soles of her shoe? - Neither, my lord Then you live about her waist (..)2015 Hamlet