Way to get a six-pack of drinks with vermouth in (3-3)
I believe the answer is:
sit-ups
'way to get a six-pack' is the definition.
(doing sit-ups can give you a six-pack)
'drinks with vermouth in' is the wordplay.
'drinks with' becomes 'sups' (to sup is to drink. I am not sure about the 'with' bit.).
'vermouth' becomes 'it' (short for 'Italian vermouth' as in 'gin and it').
'in' is an insertion indicator.
'sups' enclosing 'it' is 'SIT-UPS'.
'of' acts as a link.
(Other definitions for sit-ups that I've seen before include "Physical training exercises" , "Gym exercises" , "Tummy tighteners" .)