Load vehicle and set off (5)
I believe the answer is:
cargo
'load' is the definition.
('cargo' can be a synonym of 'load')
'vehicle and set off' is the wordplay.
'vehicle' becomes 'car' (car is a kind of vehicle).
'and' is a charade indicator (letters next to each other).
'set off' becomes 'go' (I've seen this in other clues).
'car'+'go'='CARGO'
(Other definitions for cargo that I've seen before include "Goods being transported" , "Payload" , "Goods carried by ship, aircraft" , "Shipment" , "Goods in transit" .)