Biscuits, nuts and bananas (8)
I believe the answer is:
crackers
I believe this clue is a triple definition!
'biscuits' is the first definition.
(I know this)
'nuts' is the second definition.
(both can informally mean mad)
'and' is a link.
'bananas' is the third definition.
(both can informally mean mad)
(Other definitions for crackers that I've seen before include "Crazy types" , "Biscuits; fireworks" , "Insane" , "they may be on the table at Christmas" , "Yanks open these" .)