There are some things that you should always have in your car “just in case” and can be tucked away to not tempt a break-in:
Phone charger
First aid
Water
Snacks
Battery jumper (you’ll have to charge it periodically)
Paper maps (in case of emergency) — I have AAA and they provide free paper maps
A few paper towels (for e.g. checking your oil)
I also keep a quart of oil in the car, but that might be less necessary if you have a newer model or tend to stay close to home.
Winter:
For everything else, I maintain a Advice: Car bin for longer trips