If you wear glasses, or need reading glasses, a extra set, left in the car, is a good idea.
Good Sun Glasses left in the car
Sun and bug screen
A weeks personal meds that can be packaged and left in the car. Handy if a unexpected overnight occurs
Cell phone and car charger, with a phone number list
Extra clothes, clean socks and walking shoes or boots. Clothes for colder than expected temps.
A rain jacket, rain suit, or poncho
JED flashlight with extra batteries
bottled water
Toilet paper/big baby wipes, 2 gal zip lock bags come in real handy for commutes
Good detailed, up to date road maps for at least the area several hundred miles around your driving route. A small compass can help when you aren't sure which way is the right way when lost.
A good, matching full size spare, not a small emergency 'donut" spare.
Extra car keys somewhere on you, in a wallet or taped inside your belt,. You never know when your keys may be lost or broken
Small Tool kit
A 6x9' trap will help keep you clean when doing emergency car repairs on the road.
A good book or 2 for those times you are sitting on the highway for a few hours due to construction, or a wreck stopping traffic
A small FAK with Imodium AD and pain meds in it.
A travel tooth brush, paste, and dental floss come sin handy, esp if you get something stuck in your teeth while driving.
Cash, in small bills, hidden somewhere in the car, just in case you lose your wallet/credit cards. I call it my "get home" money. I have a old photo drivers license hidden in my car.