Notice soldier eating bun that's rich (8)
I believe the answer is:
abundant
'rich' is the definition.
(associated in meaning)
'notice soldier eating bun' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'soldier' becomes 'ant' (soldier is a type of ant).
'eating' indicates putting letters inside.
'ad'+'ant'='adant'
'adant' placed around 'bun' is 'ABUNDANT'.
'that's' is the link.
(Other definitions for abundant that I've seen before include "Exuberant" , "full" , "'Copious, galore (8)'" , "Plentiful, more than enough" , "Luxuriant" .)