Quid in pocket as one leaves this trader's premises? (11)
I believe the answer is:
tobacconist
'quid in pocket' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'one leaves this trader's premises?' is the wordplay.
'one leaves' becomes 'tobacco' (I've seen this before).
'this trader's premises?' becomes 'nist' (I can't justify this - if you can you should give a lot more credence to this answer).
'tobacco'+'nist'='TOBACCONIST'
'as' acts as a link.
(Other definitions for tobacconist that I've seen before include "shop-keeper" , "Cigarette seller" , "He sells packs" , "Shop" .)