Bit of luggage for instance (4)
I believe the answer is:
case
I believe this is a double definition.
'bit of luggage' is the first definition.
'instance' is the second definition.
('case' can be a synonym of 'instance')
'for' is the link.
(Other definitions for case that I've seen before include "Box of twelve bottles of wine" , "that paperback lacks?" , "Instance - lawsuit" , "Patient - luggage" , "Item of luggage" .)