Great point Russ, Imagine if there was an accident and you got overwhelmed by vapors or somehow you are unconscious and the Ambulance arrives and do not know what you are using.
They will start looking in the truck for an MSDS Book which needs to be within reach of the driver for that reason but also if you are stopped by D.O.T. State Trooper for routine inspection or if you were speeding or have a light out, etc....
If you do not have an MSDS, they can assume worst case scenario and call out a HAZMAT Team which you really don't want to have happen and the price will be around $1000.00 per hour for service, cleanup, disposal, etc....
Much, much easier to have an MSDS Book in the truck with all chem papers there.
You also need to have all containers labeled that contain powders or liquids or you can get fined.
Sorry about the rambling, they are enforcing this stuff here in Texas already and I know 2 guys that got tickets, one was just a few hundred dollars, the other was a lot more but he would not tell me how much.