Nurse must stock them occasionally for supplier (7)
I believe the answer is:
caterer
'for supplier' is the definition.
(a caterer supplies food)
'nurse must stock them occasionally' is the wordplay.
'nurse' becomes 'carer' (I've seen this before).
'must stock' is an insertion indicator.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternate letters of 'them' are 'te'.
'carer' enclosing 'te' is 'CATERER'.
(Other definitions for caterer that I've seen before include "Provision supplier" , "One supplying cheer" , "Someone who provides food and service" , "Person who supplies food for social events" , "Refreshment supplier" .)