Bag a cash prize! (5)
I believe the answer is:
purse
I believe this is a double definition.
'bag' is the first definition.
(purse is a kind of bag)
'a cash prize' is the second definition.
(I've seen this before)
(Other definitions for purse that I've seen before include "Prize in sporting contest" , "Money - contract" , "Prize funds" , "Small pouch for carrying money, mostly by women" , "Knit" .)