Finishes drink below deck (5,2)
I believe the answer is:
packs up
'finishes' is the definition.
'drink below deck' is the wordplay.
'drink' becomes 'sup' (I've seen this before).
'below' means one lot of letters go next to another.
'deck' becomes 'pack'.
'sup' after 'pack' is 'PACKS UP'.
(Other definitions for packs up that I've seen before include "stops working" , "Conks out" , "tidies things away" .)