Literal contents of empty pockets (4)
I believe the answer is:
typo
'literal' is the definition.
('typo' can be a synonym of 'literal')
'contents of empty pockets' is the wordplay.
'contents of' says the answer is hidden in the clue.
'TYPO' is hidden within 'empty pockets'.
(Other definitions for typo that I've seen before include "Misprint" , "Thanks; good health!" , "Spelling mistake" , "Printer's error" , "Mistake in printed matter, in short" .)