When I'm travelling more than... oh.... 100 miles away, I check to make sure I've got several things with me (on your list, largely):
* road flares / warning triangles
* maglight
* toolbox w/ misc tools, spare maglight batteries, etc
* at least one blanket
* at least one full change of clothes
* emergency roadside kit (has assorted things you supposedly need in case of emergency)
* emergency medical kit (has assorted over-the-counter medications, bandages, gauze pads, etc)
* a map of where I plan to be
* jumper cables
* ice scraper
* cell phone
* spare tire
* AAA/CAA Membership
* magazines or books to keep you occupied
I always fill my fuel tank at the nearest point to my origin location, and while I'm there, I grab some food of some kind... jerky, whatever, it works. I also grab a few Gatorades. I keep the drinks I want cold in the back seat floor (no heat), and the drinks I want warm (preservation for safety) on the front passenger floor, with the blanket.
I also have a CB in my car... I like to use it when I'm on the freeway, etc... and while it's not nearly as popular as it used to be, there are still some people that use them in base locations.
On a recent road trip thru the midwest, I was stuck on the freeway, near the Indiana-Ohio border for a few hours... we eventually started to creep along. At one point, a trucker got on the air, said that he needed emergency assistance. Apparently his truck had broken down on a road parallel to the interstate earlier in the day. He had called for help, but they never showed up... his cell batteries had since died, and he had fallen asleep. His cab was cold, because the engine wouldn't run (to warm the cab)... he sounded very cold & weak. Before I could even acknowledge his transmission, another trucker said that they had the state patrol on the cell phone, and they needed his location. About five minutes later, a patrolman acknowledged the emergency on the air, and we saw a cruiser heading that way...
All of that said... it's just a checklist I mentally follow before I go anywhere very far, especially if the territory is hazardous or unfamiliar. It's like second nature to make sure it's all there. It's also a good habit to make sure that all of your belts, fluids, etc., are in optimal condition before you leave. Getting 100 miles into the middle of nowhere is not a good time to learn that your serpentine belt just broke, and that your oil needed changed 3000 miles ago.
I used to have a boost pack in the back of my SUV... I just never bought another one for my car, though I know I should (I got rid of the old one). Depends on the destination and current conditions as to whether I carry a shovel & sand or kitty litter.