Biscuits or nuts (8)
I believe the answer is:
crackers
This clue is a double definition.
'biscuits' is the first definition.
(I've seen this before)
'nuts' is the second definition.
(both can informally mean mad)
'or' acts as a link.
(Other definitions for crackers that I've seen before include "Crazy types" , "Mad - biscuits" , "Mad - fireworks" , "Yanks open these" , "Insane" .)