Any number going out for drink (6)
I believe the answer is:
noggin
'for drink' is the definition.
(small quantity of alcohol)
'any number going out' is the wordplay.
'any number' becomes 'n' (mathematical symbol for an unspecified number).
'out' indicates an anagram (out can mean wrong or inaccurate).
'going' with letters rearranged gives 'oggin'.
'n'+'oggin'='NOGGIN'
(Other definitions for noggin that I've seen before include "Snifter" , "Small amount of alcohol" , "Small measure of spirits or slangy head" , "Small measure of liquid" , "Small measure of alcohol, about 1/4 pint" .)