Item of luggage in reserve? (3)
I believe the answer is:
bag
I believe this clue is a double definition.
'item of luggage' is the first definition.
(I've seen this before)
'reserve?' is the second definition.
'in' is the link.
(Other definitions for bag that I've seen before include "Claim" , "Valise" , "Piece of luggage" , "Item of luggage; catch and kill (an animal)" , "Gladstone, for example" .)