Drivers leaving odd bric-a-brac for baker's agent (6)
I believe the answer is:
bicarb
'for baker's agent' is the definition.
(leavening agent used in baking)
'drivers leaving odd bric-a' is the wordplay.
'drivers leaving' becomes 'b' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'odd' indicates anagramming the letters.
'bric'+'a'='brica'
'brica' anagrammed gives 'icarb'.
'b'+'icarb'='BICARB'
'brac' acts as a link.
I am not very happy about this link. It may be part of another bit of the clue.
(Other definitions for bicarb that I've seen before include "Baking soda (abbr)" , "Baking soda (colloq.)" , "baking aid" , "Chemical" , "Digestive remedy (abbr)" .)