Closely fitting items to stick to, upside down (4)
I believe the answer is:
snug
'closely fitting' is the definition.
'items to stick to upside down' is the wordplay.
'items to stick to' becomes 'guns'.
'upside down' says the letters should be written backwards.
'guns' backwards is 'SNUG'.
(Other definitions for snug that I've seen before include "Intimate" , "Cosy and comfortable" , "Cosy retreat" , "Comfortabel with guns" , "Comfortable with guns" .)