Big cheese and more crackers after drink (7)
I believe the answer is:
supremo
'big cheese' is the definition.
(I've seen this before)
'more crackers after drink' is the wordplay.
'crackers' is an anagram indicator (informal term for mad).
'after' is a charade indicator (letters next to each other).
'drink' becomes 'sup' (I've seen this before**).
'more' with letters rearranged gives 'remo'.
'remo' put after 'sup' is 'SUPREMO'.
'and' is the link.
(Other definitions for supremo that I've seen before include "Person in overall charge, big boss" , "top boss" , "Person in overall charge, really the top man" , "Champion" , "Big fish" .)