They say one can't choose breakfast item in pub (6)
I believe the answer is:
beggar
'they say one can't choose breakfast' is the definition.
The definition suggests an adverb but the answer is not.
'item in pub' is the wordplay.
'item' becomes 'egg' (I have seen 'Item of food' mean 'egg' so perhaps 'item' could also mean 'egg').
'in' is an insertion indicator.
'pub' becomes 'bar' (I've seen this before).
'egg' placed into 'bar' is 'BEGGAR'.
Can you help me to learn more?
(Other definitions for beggar that I've seen before include "I need bread" , "Poor person; outshine" , "Mendicant or cadger" , "Mendicant or scrounger" , "Pauper or supplicant" .)