Drink that's left (4)
I believe the answer is:
port
I believe this clue is a double definition.
'drink' is the first definition.
(port is a kind of drink)
'left' is the second definition.
(left side of a ship - opposite of starboard)
'that's' acts as a link.
(Other definitions for port that I've seen before include "Left side of ship - red wine" , "Anchorage" , "Ship's left - Dover, perhaps" , "where one would expect water" , "After-dinner drink" .)