I will admit to having once been the kind of tradesman who drives a work van with nothing but a seat between me and the tools, material, and debris in the back. I might have behaved differently if I had seen what could happen to the contents of a van in a crash.
Metal shelving racks may absorb impact better than wood
The wooden shelves you built may feel solid, but that doesn't mean they will remain so if the vehicle suddenly decelerates. The crash test in the video above was performed with a vehicle moving at the European test standard of 50 km/hr (33 mph). The shelves probably could have been better built and more solidly attached. Still, it’s instructive to see the plywood end panels sheared in half by the force of the crash.
The video above is interesting because it shows in slow motion how a particular metal racking system deforms but doesn't fail in a crash. The toolboxes slide forward in a wave-like motion; some of them even break, but they do not fly off the shelves.
Insecure tools can be a huge hazard
You do not need to speak French to understand what is happening in the video below. Even with a bulkhead, I would not want to be the crash test dummy “driving” this van—what with the pick axe and sledgehammer flying around.
Do not be a dummy; make sure your tools are solidly secured, and put some protection between you and them—in case they ain't.