Fix-a-flat. Its compressed can of air and goo that will plug up surprisingly large punctures and keep your tire drivable to get to shop to fix. Keep 2 cans on my 4 wheeler and 2 cans in my truck.

The other carry everywhere item i have on 4wheeler and truck is the battery charger/aircompressor combo units. They sell them at any auto store or walmart. Its a battery charger that you plug in to charge and also has a built in air compressor.

Afrer a year or two of carrying both those items with me I stopped paying for AAA. Oh but also carry bags of cat liter in my car in the winter time for weight and get out of the ditch or snow pile aid. I guess add the cat liter and collapsing shovel to the winter everyday carry items.

The truth is, mechanics tools in your car are fenerally useless. You arent carrying with you every part that could ho wrong or need replacing with you, there isnt much that can go wrong that doesnt involve buying a part to fix. I spent decade and a half driving around $500-$2000 cars because it made more financial sense than buying newer vehicle. Anything broke that cost more than half the car id scrap them and buy the next. The last thing ill add is that any vehicle 5 years old or newer is guna need oem tools to fix for like 70-100% of everything that could possibly go wrong with them. Even the dumbest most common shit like swapping winter/summer tires on rim certain shops cant do any more for a bunch of makes and models because of the change in rim design without buying a new tool. Spend the money on a rolling cabnet toolbox for your mechanics tools and rolling stackable toolboxes for your home repair tools because they are things you will buy once and store a life time of tools in for decades.

Edit: add ratchet straps for anyone not redneck who wouldnt laugh at the notion of ever not already having ratchet straps in their vehicle, even for a car. Hood latch breaks-strapit, door latch or lock breaks-strapit, tailgate wont latch-strapit, muffler falls off after bottoming it out jumping the tracks-strapit, people ne3d ride to town who are gross or scummy - close ratchet in trunk and let strap free for scummies to hitch on skateboard or bike.

Flex tape or other wet seal tape for hose repair.

Channel lock and a small mixed set of worm drive clamps.

Other things I don't see mentioned: JB weld, RTV (silicone sealant), thread chasers, tire spoons, dialectric grease, all depends on the services you want to offer!

Lights. At least a headlight, though I'd also consider hanging lights that could hang from the bottom of your hood and/or a light that can be positioned to stand somewhere and shine where you need it. Sure you might have your phone on you but you might need to use both hands for things other than holding lights.

Also, if you have someone wanting to help but doing more to get in the way, you can delegate them to "hold the light" to hopefully redirect them out of the way. Just use the headlamp if they are bad at aiming the light.

Get yourself a lithium jump starter. They aren't too expensive, but mine has saved my ass heaps of times. No other car needed, just jump straight from the battery pack.

Riggers gloves, for handling anything car related at uncomfortably low or high temperatures.

A 10mm socket for emotional support

Maybe bring some air fresheners so when you're done helping someone, you can go "Here's your complimentary air freshener, thank you for choosing us!" To lighten the mood.

Snacks!

Never underestimate the power of sugar to fix an angry brain.

Compact, cig lighter charged air compressor. Once you use that tire patch kit, be able to air up their tire.

Space blanket. Hi vis vest.

This is admirable, but in which city are you often seeing people struggling with car troubles?

Pliers, wire stripper/crimper combo tool, a couple feet of random 16ga wire, and a few crimp terminals/splices. Wires are prone to being abraded, melted or chewed on by rodents and I have gotten out of a couple sticky situations by scavenging up wire for a temporary patch to obvious damage.

Depending on how much space you have on top of that, a $9 multi meter from harbor freight is also a great carry tool to determine if fuses are blown without pulling each one individually, or seeing if someone's charging system is still working.

A jumper battery that doubles as an aux phone battery would be worthwhile to have, because it has two functions, essentially. A telescoping magnet and or grabber is great for things that fall.

Anything else is bigger work steps, I think. Maybe a Bluetooth obd scanner? Though I don't think strangers will let you plug into their car, typically.

I found having a scissor jack and some stands came in handy.

diagnostic computer device