I have taken three road trips this year averaging 4,000 miles per trip. Lots of good advice above.
Take an extra car key and store it outside the vehicle out of sight so that if (when) you misplace or lose your key, you have a spare.
Set your hotel addresses in your Garmin or your device to have them identified and easy to bring up.
Make sure you have roadside assistance for your flat tire or dead battery.
Pack a gallon of engine coolant to have available if your cooling system starts leaking. Even a small leak can disable you.
Take a first aid kit (buy it or make it up yourself).
You can buy an inexpensive "emergency kit" that contains road flares, rubber cones, wet suit, flashlight, etc that will aid you if you break down in a remote area or dark road.
There's more, this is a start.
Everyone has a plan until they get punched in the mouth...philosopher Mike Tyson