Advocate a couple of drinks (9)
I believe the answer is:
supporter
'advocate' is the definition.
(supporter is a kind of advocate)
'a couple of drinks' is the wordplay.
'a couple of drinks' means two substitutions for 'drink'.
'drink' becomes 'sup'.
'drink' becomes 'porter' (porter is a kind of drink**).
'sup'+'porter'='SUPPORTER'
(Other definitions for supporter that I've seen before include "Champion" , "Second" , "Fan; heraldic figure" , "One cheers" , "Stay" .)