Like one on the wagon missing drinking can (9)
I believe the answer is:
abstinent
'like one on the wagon' is the definition.
(a recovering alcoholic or addict is 'on the wagon')
'missing drinking can' is the wordplay.
'missing' becomes 'absent' (similar in meaning).
'drinking' indicates putting letters inside (inserted letters are consumed or drunk).
'can' becomes 'tin' (both are metal containers).
'absent' enclosing 'tin' is 'ABSTINENT'.
(Other definitions for abstinent that I've seen before include "self-control" , "Not indulging appetite for food or drink" , "Restrained" , "Going without, especially food and alcohol" , "Not taking drink" .)