'Farewell', clutching one's overnight bag (6)
I believe the answer is:
valise
'overnight bag' is the definition.
(valise is a kind of overnight bag)
'farewell clutching one's' is the wordplay.
'farewell' becomes 'vale' (I've seen this before).
'clutching' is an insertion indicator.
'one's' becomes 'is' (roman numeral).
'vale' enclosing 'is' is 'VALISE'.
(Other definitions for valise that I've seen before include "A small suitcase for Leavis" , "Small overnight bag" , "Overnight case" , "Travel bag" , "Elvis A? (anag)" .)