After two drinks, this setter's game! (3,5)
I believe the answer is:
Here is my best explanation:
'game' is the definition.
(gin rummy is a kind of game)
'after two drinks this setter's' is the subsidiary indication.
I cannot really understand how this works, but
'setter's' could be 'my' (I've seen this in other clues) and 'my' is present in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for gin rummy that I've seen before include "Card game", "cards" and "A card game".)