The rest get a memento to carry (9)
I believe the answer is:
remainder
'the rest' is the definition.
(synonyms)
'a memento to carry' is the wordplay.
'memento' becomes 'reminder' (I've seen this before).
'to carry' is an insertion indicator.
'a' placed inside 'reminder' is 'REMAINDER'.
'get' acts as a link.
(Other definitions for remainder that I've seen before include "part that is still to come" , "that's left" , "Dispose of unsold copies of book at a reduced price" , "The part that is left over" , "set of unsold books" .)