Off with the car to get some seed (4)
I believe the answer is:
away
'off' is the definition.
('away' can be a synonym of 'off')
'get some seed' is the wordplay.
'get' says to put letters next to each other.
'some' becomes 'a'.
'seed' becomes 'way' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'way' is 'AWAY'.
'with the car to' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for away that I've seen before include "Non-home match" , "At a distance in space or time" , "Absent, gone" , "'''... in a manger, no crib for a bed'' (carol) (4)'" , "football result!" .)