Drink? Ordered lager (English) and a mixer (6,3)
I believe the answer is:
ginger ale
'a mixer' is the definition.
(I've seen this in another clue)
'drink? ordered lager english' is the wordplay.
'drink?' becomes 'gin' (gin is a kind of drink).
'ordered' indicates an anagram.
'english' becomes 'e' (abbreviation).
'lager' with letters rearranged gives 'geral'.
'gin'+'geral'+'e'='GINGER ALE'
'and' is the link.
(Other definitions for ginger ale that I've seen before include "Spicy, sweetened non-alcoholic drink" , "It won't make you drunk!" , "Fizzy drink" , "One drink" , "pop" .)