Abandoned in vestibule, something a traveller may carry (7)
I believe the answer is:
holdall
'something a traveller may carry' is the definition.
'abandoned in vestibule' is the wordplay.
'abandoned' becomes 'old'.
'in' is an insertion indicator.
'vestibule' becomes 'hall' ('hall' can be a synonym of 'vestibule').
'old' inserted within 'hall' is 'HOLDALL'.
(Other definitions for holdall that I've seen before include "Large carrying bag" , "A large soft travelling bag - stuff everything in" , "Large bag (no need for another?)" , "Large case, with handles" , "Handled bag" .)