As more than a few people have commented on my tack box in past weeks, I post these here for a wider audience.

I got tired of arriving at a barn only to spend 10 to 15 minutes scrounging up brushes, hoof picks, &c., so I put those in a bag.
Then I bought my own saddle, with the changeable gullet, so I wouldn't have to ride those school saddles that feel like two angle-irons welded to an old oil-drum. The changeable gullet meant I could fit any horse I was given in only a few minutes... but then I got tired of tossing the saddle into the back seat of the car/station wagon/truck and having to lay it on the ground...

So I made this:

It has two compartments, and the dimensions are: as long as my saddle, and just high enough to keep it off the ground.

And it fits perfectly under the tonneau cover of the truck:

One  final note: the middle-piece has a hole cut out. That's to create a support for the bottom of the  box, as well as a divider between the two compartments.