I don't see the point of having all this stock in your truck idea. I keep a general assortment of items for service calls that I don't use for regular jobs.
A service call to me is a job that is not planned out and needs quick attention.
Bad breakers, plugs or switches or just a something not working call.
I worked out of a pick up for years and now out of a van. The van just makes me carry more stuff I don't need.
Now if I was working out in the boon docks I may have a different opinion but a supply house is a stones throw away for me.
