I use something like this for one toolbox:
Trademark ToolsT Stackable Mobile Tool Box with Wheels: Other Home Improvement : Walmart.com
On mine, the front of the bottom slides open for easy access.
The top keeps squeegees/t-bars/scrapers/soap. The bottom holds my “sharps” and rubbers box, boabs, and WFP brushes.
Then I have one of these:
Husky 22 in. Cantilever Plastic Organizer with Metal Latches-17185073 at The Home Depot
Which I call the Pure Water box.
The top organizer holds all sorts of jets, connectors, knickknacks and doodads. The bottom, stuff like whack adapters, reach arounds, extra hose parts, marine putty and the such.
Finally, I have one of these:
Husky Bucket Jockey-82045N12 at The Home Depot
Which I cut down the seam and screwed to the side wheel well of my trunk. Holds all the random stuff like channels, muggle tools, etc.
These 3 items live on the left side of my trunk. On the right side I strap my DI tank to the back of the seat, keep my hoses and poles and keep the “dirty” rag bucket.
Clean rags and strip washers live on the back seat in a nice pile.
This setup is for a Ford Exploder, but I hope it helps.