Also a nice tip, lube the locks (lockspray) and door seals (the door grease (?) stick thingy). Keep them from freezing and smoothly operating.

super cold in Minneapolis and for the first time in a couple years i'm seeing cars jump started.
so i'm back from getting grocerys and a car has its hood up and the driver is using some sort of compact starter kit from what I can see.thats fine but the kit came with a warning traffic cone and its placed just where it should behind the car.problem----it's the size of a pop can! I guess to fit in the little case the charger came in there was not enough room for anything larger.
in the middle of a cold bright day I could see it but dark and stormy,no chance and with a dead battery the car won't have any flashing warning lights or headlights on.
the point being find yourself a better warning cone/light/flare or whatever and keep it in the car.you could turn that little kit cone over and have drink out of it while the car is warming up!

I have and recommend a Reflective Triangle in my trucks parts and tools kit, right next to the jumper cables.

LED Flares work well too.

Regarding car keys and assuming at least one of the doors has a mechanical lock cylinder (only the driver's door on my car has one; most cars these days rely on the electronic key fob to unlock/lock) you can have an ordinary key cut to unlock the door to gain entry. Hide a chip key somewhere inside the car to drive. Then the ordinary key can fit your EDC easier. Make SURE the ordinary key unlocks the door BEFORE you leave the dealership or where ever you got the key cut.

Keep in mind that hiding the chip key too near where it needs to be read can disable the antitheft system when you don't intend to. What's "too near"? I don't know. Probably best to experiment carefully with your car.

Also, I've heard that some insurance companies will deny auto theft claims if you can't produce all the keys on demand.

For what it may be worth:
In Germany the reflective triangle is considered important enough to be mandatory on the car. LEOs can fine you if you can´t produce one on demand.

After a recent hike, I found that my chip key somehow got smashed in my pack and fell apart. I could use the key part of the fob to open the driver's door, which is the only one that has a mechanical lock cylinder, but I couldn't reassemble the rest of the pieces properly and it wouldn't start the car. Thankfully, I had another in my EDC purse, which was left in the car for the hike. We bought our car used so didn't get a valet key, but I had a couple made last week, and one now lives on my hiking lanyard for adventure time.

I do worry a little about leaving a fob in car, but it's an older car and doesn't have a fancy alarm or that proximity alert-thingy that new cars do.

Faraday cage (tin box) for the chip?

Does the trunk open with a physical key? One of those magnetic key storage cases could securely hide a key inside your trunk indefinitely and if a physical lock can access it, there you go.

Just thinking out loud, I have only mechanical locks and my third key is identical to the other two, it is not coming apart.

adding small (1 aa) battery tactical flashlights.