Sweet Chariot is a brand of chewing sugar cubes that come only in catering packs. Dan Dreiberg had packs in his house and whenever Rorschach visited his home he used to steal some of them from and keep them in his pocket and chew them. Sugar cubes were found in his pocket during his arrest.
Steven Fine paid a visit to Dreiberg and noticed a bag of the sugar (no doubt making a connection with the cubes found on Rorschach during his arrest). When Dan rescued Rorschach from Sing Sing, he put a bunch in his pockets before leaving and escaping the police force.
It is not clear in the narrative if the brand is owned by Veidt Enterprises.
The name is perhaps a reference to the spiritual song Swing Low, Sweet Chariot.