+1 on the self-fusing silicone tape. AKA Mox tape, it can be used as a way better option for anything electrical, and is also weatherproof for off-label uses. Might even help plug a leaky hose.
I carry a quart of spare oil and ATF for long trips. There's a gallon of drinking water stashed in every vehicle I own for either human or mechanical emergency, lesson learned as a desert-dweller.
Small tube of black RTV, factory sealed.
Small, med and large hose clamps. Fuel, heater, and rad hose sizes.
The utility:volume ratio for a 12V test light can't be beat. Hard to believe such a small, simple tool can diag most of the electrical issues you'll ever have.
I always have a Victorinox multitool on my belt which is great at supplanting the need for a box full of screwdrivers. Has blades, saws, and real pliers too, but obviously size limited. If I have to, I can bash things with it.
Spares of unique parts that either have failed in the last 25 years, or might and are not going to be easy to find at the FLAPS. Example: MSD HEI module.
Suitable tire changing tools are often overlooked. I carry a large star wrench in the truck. No one wants to try for 140 lb-ft using a sketchy OE emergency tool that's 10" long.
Any other special tools you might need for foreseeable road maintenance or adjustments that aren't likely to be found, scrounged or borrowed.
Tow strap, which includes points on front and rear of your vehicle to attach it (read: be prepared to use it). I also keep a 6' length of GR70 5/16" chain with slip & grab hooks in the truck.