I am very into Naturopathic medicine...that is the route I have chosen for our family, so you'll notice the products in mine are different.
Start with a sturdy container with a lid that stays closed so it doesn't spill everywhere. I like the plastic because you can wipe it off when stuff gets spilled on it in the car.
Of course, an assortment of band-aids are a must
Peroxide in a travel bottle, healing cream, cotton balls and first aid supplies
We hike alot, so I've got TP, and toilet seat covers for those nasty out-houses.
Also matches and those little pulse point wrist bands for car sickness.
Bug stuff. A big one for around here in the summer
Sunscreen, Face Sunscreen and After Sun
This is a big deal for me...I'm a tea snob...I can't drink bad tea, so I'm always ready.
Nail File, sewing kit and little scissors (all from the $1 store) You can't imagine how often I use these silly little scissors in the car. They are pretty durable for cheap baby scissors.
Of course Advil and Tylenol is a must. For stomach issues we take Papaya enzyme. It's found in any health food store or section of a store and works fantastic. They are chewable and taste great so kids like them. Also EMERGEN-C when someone starts to feel under the weather boosts immunity, then of course Benedryl and allergy tabs. My husband and my son are allergic to pet hair so it really helps to have Benedryl on hand if we end up at a "Pet House"
The "unmentionables" that I will mention. You need these feminine items in the car.