Drink pop (3)
I believe the answer is:
nip
I believe this clue is a double definition.
'drink' is the first definition.
(I've seen this before)
'pop' is the second definition.
('nip out' and 'pop out' can both mean to go out)
(Other definitions for nip that I've seen before include "Pinch sharply, perhaps in the bud" , "small draught" , "Dash" , "Touch of frost" , "Swift bite" .)