Bill wears accessories (3-3)
I believe the answer is:
add-ons
'accessories' is the definition.
(I've seen this in another clue)
'bill wears' is the wordplay.
'bill' becomes 'ad' (advertisement stuck on wall).
'wears' becomes 'dons' ('don' can be a synonym of 'wear').
'ad'+'dons'='ADD-ONS'
(Other definitions for add-ons that I've seen before include "Additions" , "Accessories" .)