We don't have synonyms for sag wagon yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are stage wagon and g wagon.
(n) :
A truck, van or other support vehicle used during cycling events, designed to hold food and other equipment for participants, and to pick up and carry any cyclists (and their bicycles) who can no longer ride.
(n) :
A truck, van or other support vehicle used during cycling events, designed to hold food and other equipment for participants, and to pick up and carry any cyclists (and their bicycles) who can no longer ride.