A lot of money in a carton (6)
I believe the answer is:
packet
This clue is a double definition.
'a lot of money' is the first definition.
(I've seen this before)
'carton' is the second definition.
(I've seen this before)
'in a' acts as a link.
(Other definitions for packet that I've seen before include "Package - large amount - boat" , "bomb" , "Container - ship" , "Paper/cardboard container" , "A boat; large sum of money" .)