Blanket for one remaining in coastguard stores (8)
I believe the answer is:
covering
'blanket for one' is the definition.
(blanket is a kind of covering)
'remaining in coastguard stores' is the wordplay.
'remaining' becomes 'over' (as in 'we ate them all but had one over').
'coastguard' becomes 'cg' (abbreviation for coastguard).
'stores' means one lot of letters goes inside another.
'over'+'in'='overin'
'overin' placed inside 'cg' is 'COVERING'.
(Other definitions for covering that I've seen before include "making new version of record" , "Protecting" , "shelter" , "Sleeve" , "Enveloping" .)