Keeping a key to get into the shop (7)
I believe the answer is:
storage
'keeping' is the definition.
(storage is a kind of keeping)
'a key to get into the shop' is the wordplay.
'key' becomes 'g' (I've seen this in other clues**).
'to get into' indicates putting letters inside.
'the shop' becomes 'store' ('store' can be a synonym of 'shop').
'a'+'g'='ag'
'ag' inserted inside 'store' is 'STORAGE'.
(Other definitions for storage that I've seen before include "- Heater; - battery" , "Space available for keeping goods" , "Charge for warehousing" , "Depository space for goods" , "reservation?" .)