A few years ago I was working in someone else's shop. Out of frustration, I put together this tool box of mostly spare tools to take with me. I keep it in the back of my Toyota, mostly so I have tools to help someone else or for going to the junkyard. I recently freshened it up-
It is stored in a HF plastic case with inside dimensions of about 9x12"

The the tools that I'm likely to use first/most often display when you open the box. It seems like the Leatherman solves a lot of problems and this is a good place to keep it where I can find it. All my flashlights use 18650 batteries now and I keep a couple of spares if I need them. There's a couple dollars of quarters for the coke machine at the junkyard and maybe enough for the admission fee to the yard at the PinNPull (A few of these tools I've actually found at junkyards over the years)
There's a couple of storage cavities in the lid - one for zipties and the other for stainless safety wire
The foam is the stuff they sell at Harbor Freight and it supported by an aluminum sheet metal tray. Here's the tool pallets unloaded from the box. When I've used this at the junkyard, I typically lay it all out on a hood or a trunk to work.
The bottom of the box contains a 3/8 drive socket set - all the sockets are cats and dogs and I need to come up with some marking for sizes.
I don't troll junkyards as much as I used to, the Toyota never causes any issues and it seems like the most use it gets is when I'm visiting my kids and they're asking Dad for help fixing something.