Leftover, remaining (8)
I believe the answer is:
residual
I believe this clue is a double definition.
'leftover' is the first definition.
(I've seen this in another clue)
'remaining' is the second definition.
(I know that remaining can be written as residual)
(Other definitions for residual that I've seen before include "Leftover - used rail (anag)" , "'Remaining, left over (8)'" , "Remaining at the end" , "Leftover; repeat royalty" , "Remaining; repeat royalty" .)