Not a day patient’s bag? (9,4)
I believe the answer is:
overnight case
'bag?' is the definition.
(overnight case is a kind of bag)
I don't understand how the rest of the clue works.
(Other definitions for overnight case that I've seen before include "One has brief stay in hospital" , "Small item of luggage" , "Item of luggage for short stay" , "It may be packed" , "Bag" .)