Regularly snaffled cash box (4)
I believe the answer is:
safe
'cash box' is the definition.
'safe' can be an answer for 'box' (safe is a kind of box). I am not certain of the 'cash' bit.
'regularly snaffled' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
The alternate letters of 'snaffled' are 'SAFE'.
Can you help me to learn more?
(Other definitions for safe that I've seen before include "Strong metal box to store valuables" , "Iron box in which to keep money or important papers" , "Strongbox; secure" , "Secure - place to keep cash" , "Metal box for storing valuables in" .)