Food in car? Rotten (6)
I believe the answer is:
carrot
'food' is the definition.
(carrot is a kind of food)
'car? rotten' is the wordplay.
'rotten' becomes 'rot' (I can't justify this - if you can you should give a lot more credence to this answer).
'car'+'rot'='CARROT'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for carrot that I've seen before include "veg" , "Rewarding vegetable?" , "Incentive (but not the stick)" , "Vegetable to entice the donkey" , "Obstacle in race" .)