Cereal bargains the regulars picked out? (4)
I believe the answer is:
bran
'cereal' is the definition.
(type of cereal)
'bargains the regulars picked out' is the wordplay.
'the regulars picked out' indicates alternate letters (letters picked out at regular intervals).
The alternating letters of 'bargains' are 'BRAN'.
(Other definitions for bran that I've seen before include "Husks after milling" , "Husks of cereal seeds sifted from flour" , "Health food" , "Healthy breakfast" , "Refuse from grain" .)