Do municipal trucks need to have fire extinguishers?
Yes, vehicles that would be considered commercial vehicles need to have a fire extinguisher (see link for a list of items needed during a commercial vehicle inspection).
The Federal requirement is that the extinguishers need to be rated at least 5BC for non-hazardous vehicle classifications.
Note: There may be exceptions for local vehicles
Federal motor carrier safety regulations; General § 390.3
Federal motor carrier safety regulations; General § 390.9
Resources
49 CFR 393.95 Subpart H (pdf)
U.S. Government Publishing Office (GPO)
January 2015