Primarily sold packed lunches in fast food joint (6)
I believe the answer is:
spliff
'joint' is the definition.
(I've seen this before)
'primarily sold packed lunches in fast food' is the wordplay.
'primarily' suggests taking the first letters.
The initial letters of 'sold packed lunches in fast food' is 'SPLIFF'.
(Other definitions for spliff that I've seen before include "Dodgy smoke" , "Marijuana cigarette" , "Pot cigarette (colloq.)" , "Reefer (colloq.)" , "Blow in this tube" .)