Sandwich unfinished but remains fresh (9)
I believe the answer is:
submarine
'sandwich' is the definition.
(submarine sandwich is a kind of sandwich)
'unfinished but remains fresh' is the wordplay.
'unfinished' means to remove the last letter.
'fresh' indicates an anagram (a fresh re-ordering of the letters).
'but' with its final letter taken off is 'bu'.
'bu'+'remains'='buremains'
'buremains' with letters rearranged gives 'SUBMARINE'.
(Other definitions for submarine that I've seen before include "... underwater craft" , "snack" , "U-boat" , "Underwater (vessel)" , "Submersible warship" .)