This is my protocol at work for our Motor Coach's, no placard or endorsement.
You could probably carry more than my limits because you don't have the passengers.
We transport a lot of Air National Guard personnel.
Buses may carry small arms ammunition labeled ORM-D, emergency hospital supplies
and drugs. You can carry small amounts of
some other hazardous materials if the
shipper cannot send them any other way.
Buses must never carry:
Division 2.3 poisons, liquid Division 6.1 poisons,
tear gas, irritating materials.
More than 100 lbs. of solid Division 6.1
poisons.
Explosives in the space occupied by people,
except small arms ammunition.
Labeled radioactive materials in the space
occupied by people.
More than 500 lbs. total of allowed
hazardous materials, and no more than 100
lbs. of any one class.