Delivery agent returned earthenware vase, filling bottles (9)
I believe the answer is:
lifesaver
'delivery agent' is the definition.
(delivery can mean rescue)
'returned earthenware vase filling bottles' is the wordplay.
'returned' says the letters should be written backwards.
'bottles' indicates the answer is hidden within the clue (bottling is a kind of containing).
'revasefil' is hidden within 'earthenware vase filling'.
'revasefil' backwards is 'LIFESAVER'.
(Other definitions for lifesaver that I've seen before include "Something that comes to one's aid at a critical moment" , "Vital help when in serious difficulty" , "Mae West perhaps" , "One who'll help" , "vital resource" .)