Sorry, it took me awhile to stop laughing. 'bout the only thing I've ever put any thought into taking on a road trip is me. Just get in the car and go.
Last I heard Alabama, Louisiana, Mississippi, Oklahoma, Texas, New Mexico, Arizona and most parts of California have auto parts stores, mechanics, tow trucks and just about anything else you'd need.
Then again, all this advice might convince you to buy a pickup.
Back in '07 and '08 when I went on two cross-country road trips in my stock '55 Chevy pickup, I took:
These items in the cab: Cellphone, AAA+ membership, reading glasses, my lucky WWII Army Air Corps mechanics cap, cheap aviator sunglasses, small cooler with water and trail mix.