1) Money and good maps. (ATM cards and credit cards too).
2) Sunglasses, spare glasses.
3) enough snacks / drinks / water for a day.
4) warm clothings inside the car, not in the trunk.
5) basic first aid kit, including basic medications for cold, headache (dont bring asprin), stomach, bandaids, antibiotic ointment, alergy treatment... sterlized gauge, cotton swap, wraps, pads.
6) since you are driving, you can bring a paring knife and a peeler - for fruits and veggies you may pick up on the road. Important to eat your veggies and fruits when travelling.
7) DO NOT OPEN YOUR TRUNK AT PARKING LOT THEN LEAVE YOUR CAR. IF YOU NEED TO GET SOMETHING FROM YOUR TRUNK, DO IT AHEAD BEFORE YOU REACH YOUR INTENDED STOPPING PLACE. The point is you dont want some bad guys seeing you have stuff in the trunk and then you locked the car and walked away. It only takes 30sec for the thieves to break into your car and rob you clean.