Leave car, put on a jacket (5)
I believe the answer is:
parka
'jacket' is the definition.
(I know that parka is a type of jacket)
'leave car put on a' is the wordplay.
'leave car' becomes 'park' (I've seen this before).
'put on' says to put letters next to each other.
'park'+'a'='PARKA'
(Other definitions for parka that I've seen before include "cover plus hood attachment" , "Hooded warm jacket" , "weatherproof cover" , "Hooded garment" , "Hooded waterproof coat" .)