Yankee's after a mixer for drink (6)
I believe the answer is:
whisky
'drink' is the definition.
(whisky is a kind of drink)
'yankee's after a mixer' is the wordplay.
'yankee' becomes 'y' (phonetic alphabet: alpha, bravo, charlie etc.).
'after' means one lot of letters go next to another.
'a mixer' becomes 'whisk' (whisk is a kind of mixer).
'y' put after 'whisk' is 'WHISKY'.
'for' acts as a link.
(Other definitions for whisky that I've seen before include "Alcoholic drink" , "W in radio alphabet" , "reportedly available for Thin Lizzy gig?" , "Grain alcohol" , "Scotch" .)