Egghead gets in a quick banquet (5)
I believe the answer is:
feast
'banquet' is the definition.
(I know that banquet can be written as feast)
'egghead gets in a quick' is the wordplay.
'egghead' becomes 'e' (head letter of 'egg').
'gets in' is an insertion indicator.
'a quick' becomes 'fast' (I've seen this before).
'e' going within 'fast' is 'FEAST'.
(Other definitions for feast that I've seen before include "Lavish meal" , "entertainment" , "wine and dine" , "Sumptuous meal" , "lots of food" .)