Many thoughts and stories could be had in the Greasy Spoon swapping roadside stories Im sure!!
In my mind the kit is dependent on these variables: How far do you have to drive and will you be going on back roads or interstate? Will you be driving at all at night? What shape is the truck in to begin with (an ounce of prevention, etc). Off the top of my reeling mind and with the hope that you never need:
1. fan belt.
2. silicone you mention like mega copper or similar gasket in a tube? Yes.
3. JB Weld or similar type epoxy pookie.
4. Fire Extinguisher
5. Flashlight
6. 30w oil
7. tools?...channel locks, c wrench and vise grips go a long way.
8. Gas can.
9. Patience and a sense of humor.
With that I remember springing a water leak in Texas and using black pepper to seal it up!
"All broken down by the side of the road, I never felt so alive or alone". Tom Waits.
Happy Trails!