An Ideal Toolkit. Small size, not the whole cupboard...

Or, as the commercial use to say; "Some days you feel like a nut, some days you don't."

All I have to add is this:

Beef jerky. Lots and lots of beef jerky.

And about a gallon of water.

when a crisis happens, sometimes you need a snack to get your head back straight.

caramels muffle the swearing.

also in my parents' Jeep, there was a spare distributor rotor.

when I bought my motorcycle the ex I like to badmouth told me that I shouldn't have paid more than a dollar a cc for it. then she told me I needed to carry a tool kit for when it broke down.

I declined to tell her that there was a connection between paying more than a dollar a cc and not needing to carry a tool kit.

For your tool kit I suggest these additions:

A couple of knives (box cutter and one other good knife, at least) and pair of good scissors in the tool kit.

Two or more small LED flashlights. Say what you want about Harbor Freight, but they give these away with any purchase and their coupon, and they're excellent, as they have a hook and magnet on the back. I pick them up every time I can, as they give a surprising amount of light for such a small device, with decent battery life. They're small enough to use in the smallest, tightest work areas.

Two medium size Crescent wrenches, one for each end of the bolt your box wrench won't fit.

Stubby hammer (or full size, if you've the space).

At least one pair of heavy duty work gloves, and a box of 100 disposable nitrile gloves.

One pair safety glasses, the universal kind that fit over everyday glasses.

A can of Fix-A-Flat. Although I prefer to change a flat tire in the traditional manner, you can get stuck in a situation where your jack or you aren't able to do the job. I was once, and now carry a can just in case.

Six 20 minute road flares.

Duct tape. If you have to ask, you don't understand, and I'll refer you to a couple of MB episodes.

Because I live in earthquake country, I have a survival kit, with these additional items to the ones others have mentioned:

A small 12V DC/AC inverter so I can have line level power off my battery to run anything I might have grabbed in an emergency. It has a USB output as well to charge cell phones. It's about the size of a hardbound book.

A solar/spring wound crank powered AM/FM radio. Your car battery won't last forever. I think I have to replace the current one, as the new ones have that USB output again.

As for food supplies, I went down to the local surplus store and picked up three day's worth of emergency food and water from their boating supply section. Consisted of a lot of little pouches of water, and a couple of bricks of USCG approved "Emergency Food" with a 5 year shelf storage life. I tucked them away in a small bag in the depths of the spare wheel well. When the last batch expired, I tried both. The water was tasteless, and the food was horrible, but edible.

A couple of space blankets (mylar survival type). They fold up into the size of a fist. Since I usually am travelling with others, I keep extras just in case. Mine are bright orange on one side to increase visibility.

An old hoodie sweatshirt. I live in California, where microclimates mean that even during the summer, you need warm clothing (especially in the mountains at night).

A super high tech drinking filter. I got it from a backpacker supply store, on recommendation from a friend who does a lot of back area camping. It will supposedly allow you to drink from any water source without fear. Because it's designed for backpackers, it's small.

One piece of emergency gear I carry on my key ring: ResQMe. It's small, but it'll break a car window and cut a seat belt.

May I issue a ***WARNING*** to anyone using such.
[I may have said this before}
If you do need to use such, you have less than 12 hrs, no more than 24 hrs at the very worst, to get your wheel cleaned.
That stuff is glue.
And it sticks.
When used, it "welds" the tyre to the wheel, in such a way, that often the only way to part the two is cutting.
"Alloy" type rims are trashed in this case, you will damage the wheel when cutting the tyre off.
More on Alloy than steel, because the weld to Aluminium is stickier for some reason than steel.

Therefore, if you MUST use it, only use it as far as the next place you can get the tyre cleaned and replaced.
Immediately.
Do not "It can wait until morning" on it, do it sooner rather than later.

This warning comes to me from a couple of mates of mine who spend their lives doing tyres, and have had to deal with a few customers "Here, have the wheel back, try yourself, if YOU cant shift it, no one here can" after cutting most of the tyre away to leave the wheel with a lot of tyre and adhesive that wont shift whatever you use.

They ESPECIALLY decry the use on large HGV wheels, because once used, its always "Somebody else's problem" and only ever comes to light when a few months later that tyre-weld has set to its maximum.

On steel, you can just about sand down the tyre-weld and tyre mix, given enough time, but the easier quickest and often cheaper option is buy a new wheel.

YES have a can for extreme events where maybe you have one more punctures than spare wheels carried.
But be prepared to either sacrifice wheel and tyre, or get it cleaned out again quickly, and get the puncture professionally dealt with.
By this time it has ruined the day already, so dont bemoan fate, at least you didnt have to walk or wait for a tow van?.

although I've made more than a few threats to use it in small equipment tires - by which I mean the wagons, carts, or tool dollies that for some reason they think it is a good idea to use a tubeless tire instead of a solid fill tire - and the tire shops no longer want to spend the time to do a solid fill on tires so small.

if I could get the tires on the chipper reduced to a slow leak, that would be progress. if I could get them to seat to the rim at all, that would be progress. maybe some experimentation with a ratchet strap and some green slime is in order. I've also considered expanding foam, since the chipper is light enough to even roll on completely deflated tires. - pull the valve core and fill through the stem, then cap the stem. - but I have to get the beads to seat before I can do anything.