Rolling Stone who bought sandwiches (4)
I believe the answer is:
hobo
'rolling stone' is the definition.
(I've seen this in another clue)
'who bought sandwiches' is the wordplay.
'sandwiches' indicates the answer is hidden within the clue (the answer is sandwiched in by the clue).
'HOBO' is hidden within 'who bought'.
(Other definitions for hobo that I've seen before include "Homeless American" , "Vagrant (US)" , "Itinerant" , "Tramp (US)" , "Bum" .)