FIRE:
Personnel Transports - In case you don't want send another engine or whatnot and extra personnel to scenes. If I wanna finish a call quickly I send more engines or whatever is required more. Could be a 6x6 General transport or an SUV or even a Humvee. Companies in my area use old command units just for sending more firefighters on scene if the engine can't hold them.
POLICE:
Police Morotcycles - Can have 1 Officer. Gets to scene faster but cannot transport prisoners. Kinda like the Fly-Car that cannot transport a patient.
Prisoner Transports - Like the Mass Casualty but for prisoners instead. This has most likely been brought up before.
Heavy SWAT Transports - Holds double the amount of a basic SWAT Truck but costs more like 19,000 Credits or so.
Police Boats - For any missions requiring police presence in water. For instance a Stolen Yacht, Drug Bust On Yacht, Suspect Drowning which could require a fire boat, police boat, and an ambulance.
Heavy Police/SWAT Rescue Units - Manned by police officers/SWAT officers that can assist in accidents that require a heavy rescue. Police officers would need Rescue Training though which could be a training idea as well.
Call could be a collapsed building that have armed suspects and hostages so firefighters can clear wreckage along with trained police/SWAT officers. Unit could be 19,000 Credits or so. Combination Unit yes I know but I see these at times often known as ESU Units.