System which pays out with interest, that’s handy for shoppers? (4,3)
I believe the answer is:
tote bag
'that's handy for shoppers?' is the definition.
(type of bag which a shopper might use)
'system which pays out with interest' is the wordplay.
'system which pays out' becomes 'tote' (short for totalizator betting system).
'with' is a charade indicator (letters next to each other).
'interest' becomes 'bag' (I've seen this before).
'tote'+'bag'='TOTE BAG'
(Other definitions for tote bag that I've seen before include "Large personal carrier" , "Large shopping receptacle" , "Shopper" , "Large carrying container for, eg, shopping" , "Holdall" .)