Bananas in crate for sure (7)
I believe the answer is:
certain
'sure' is the definition.
(I know that sure can be written as certain)
'bananas in crate' is the wordplay.
'bananas' is an anagram indicator (informal term for mad).
'in'+'crate'='incrate'
'incrate' anagrammed gives 'CERTAIN'.
'for' is the link.
(Other definitions for certain that I've seen before include "Known beyond doubt" , "Unquestionable" , "bound" , "Convinced" , "Nice art (anag)" .)