Item getting rolled gold on the outside is so long (5)
I believe the answer is:
adieu
'is so long' is the definition.
(both can mean goodbye)
'item getting rolled gold on the outside' is the wordplay.
'item' becomes 'eid' (I can't justify this - if you can you should believe this answer much more).
'getting rolled' shows that the letters should be reversed in order.
'gold' becomes 'Au' (Au is the chemical symbol for gold).
'on the outside' indicates putting letters inside.
'eid' reversed gives 'die'.
'die' placed inside 'au' is 'ADIEU'.
Can you help me to learn more?
(Other definitions for adieu that I've seen before include "So long abroad" , "Farewell (French)" , "A valediction" , "Goodbye, mon ami!" , "Parting word" .)