Fruit regularly seen in doctor's bag (4)
I believe the answer is:
grip
'bag' is the definition.
('grip' can be a synonym of 'bag')
'fruit regularly seen in doctor's' is the wordplay.
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'seen in' indicates putting letters inside.
'doctor' becomes 'gp' (general practitioner).
The alternating letters of 'fruit' are 'ri'.
'ri' going within 'gp' is 'GRIP'.
(Other definitions for grip that I've seen before include "Engage" , "Hold fast" , "Domination" , "Ditch" , "Fascinate" .)