Said to be fed up about the end of the banquet (6)
I believe the answer is:
stated
'said' is the definition.
('state' can be a synonym of 'say')
'fed up about the end of the banquet' is the wordplay.
'fed up' becomes 'sated' (sated can mean completely fed).
'about' is an insertion indicator.
'the end of' indicates one should take the final letters.
The final letter of 'banquet' is 't'.
'sated' enclosing 't' is 'STATED'.
'to be' acts as a link.
(Other definitions for stated that I've seen before include "Uttered, expressed in words" , "Declared as fact" , "Clearly expressed" , "Expressed in speech or writing" , "Set forth (in words)" .)