Renske5060 said:
"Water."

TannedCroissant replied:
"This is excellent advice, it’s even better if you combine it with a water bottle."

kattrapp said:
"Blanket."
 
benwinsatlife replied:
"Blankets are important if you break down in a cold rural location, but also if you get too lit at the party you can sleep it off before driving home."

"A fire extinguisher. About 2 years ago I was in the car with my parents when all of a sudden the gears stopped responding and smoke started coming out of the front and back. We parked on the side of the road, opened the front, and a piece (I think it was the battery) was burning. It was only put out because a man who was passing by riding a motorcycle quickly stopped, took off his jacket, soaked it in water from a bottle that he had with him, and covered the fire with it. Turns out he was an ex-fireman. You probably shouldn’t always count on being that lucky."

pixelunicorns said:
"First aid kit, maps, and emergency supplies."

Zemu_Robinzon replied:
"In my country, you're legally required to have a first aid kit in a car."

Random_Dude81 replied:
"...and a basic first aid knowledge including CPR to get a driver's license."

"Lot less practical but a lot higher quality of life thing; sunglasses."

barefoot-bug-lover said:
"If you travel with your dog, a bottle of water and a drinking bowl."

johnnycakeAK replied:
"And a bag with some spare food for the dog. My truck has at least 3 days' worth of food for my dog at all times."

D4m0n619 said:
"Jumper cables."

User replied:
"This. It’s even better if they are connected to a fully charged battery so you don’t need another car."

Gentlegiant33 said:
"Ice scraper/snow brush... where are my MN peeps at?"

BoredRedhead replied:
"And why is this not mandatory in an “Up north” rental car?!? One company always leaves one, some don’t. Now I have to bring my own on business trips."

dannycolaco14 said:
"Rain jacket, umbrella, change of clothes."

ScaryBilbo replied:
"A change of clothes is more than convenient, plus they go well with any survival/hygiene/aid kit..."

User said:
"Yourself. Wear your seatbelts."

goddessoftrees replied:
"Seatbelts LITERALLY save lives. I was in a serious accident back in November, where my SUV flipped 4 times down a hill and onto a creek bed, finally being stopped by a tree. I would literally be dead without my seatbelt holding me in while the SUV flipped. I was astounded when talking about the accident after the fact at how many people I know that said they didn't wear their seatbelts."

"Feels kinda random, but I hate when I’m in someone else’s car and they don’t keep a box of tissues and/or napkins in their car."

kukukele said:
"Phone charger."

TheGuyOnTop replied:
"A "spare" charger. One that you know it's in good condition and will work in case of emergency. Chargers in a car tend to get beat up and fail."

PagantKing said:
"Dashcam."

GodOfThunder101 replied:
"Front and back dash cam."

"I cannot stress this enough. Toilet paper."

"Canadian here: A candle and some matches. If you're stuck on the road during winter, a candle can heat your car while you wait for the CAA/AAA."

"Road flare, the red tube that's essentially a giant match to warn people up the road you've broken down."

"A fake coin thingy for shopping carts!

Edit because it struck me that this is not common everywhere - in Europe you often need a €1 coin to release a shopping cart for use in supermarkets etc, which you get back when you return the cart to the right place. And you usually can never find a coin when you need it. So people often have little plastic discs or keychains that hold a metal disc the same size as a euro. Very useful."

"A GPS tracker. They’re getting cheaper and cheaper and even low-value cars get stolen now. Crooks steal them and break them apart to sell bits and pieces on eBay."

"A big shopping bag for when you yet again didn't bring one from home."

"Wet wipes, especially if you have kids."

"Plastic bags. You never know when someone is gonna be sick."

Yes1tsMe said:
"A reflective vest. For when something happens to your car at night, for example, a flat tire. Put the vest on before you leave the car so you don’t get hit by another car."

Veinti_Cuatro replied:
"I work at a trauma hospital and at least one every few weeks someone is hit by a car cause they aren't visible when outside of the vehicle."

User said:
"Tool kit."

jawz replied:
"For the toolkit make sure you have every tool you need to install the spare wheel. Don't just assume they are there. I've known a few friends who got stranded this way."

"An air compressor for the tires. If your tires are deflating slowly, topping them off will allow you to reach a tire shop without damaging the rim."

"Spare tire."

the-camster said:
"An escape tool.

At least $50 in cash."

Introvert_Petrolhead replied:
"I second this.

You get one for fairly cheap and the one I have also comes with a built-in seatbelt cutter at the bottom end.

I hope I’m never in a situation where I need to use it, but knowing I have it in my car gives me some sort of tranquility lol."

"A dog collar & a leash. I once came across a stray dog in the middle of the street as I was driving home on a pitch-black rural road... I was lucky enough to be able to pull over and grab the dog before he got hit by a car - he was small enough to pick up. I walked to several of the closest houses to see if they knew whose dog he was. No one knew. So I brought him home and called the local SPCA and was able to reunite him with his owner the very next day. Anyway, it made me think, what if it was a big dog that I couldn't pick up? Would I have been able to help? And a flashlight would have been helpful to approach more of the neighbors' houses. Although this hasn't happened again, I'm prepared if it does..."

"Hand sanitizer (so you can clean your hands after handling a gas pump)."

User said:
"Flashlight."

MAGA_WALL_E replied:
"And batteries. Batteries IN a battery CASE. Not a Ziploc."

"Ibuprofen, floss picks, hair ties, and what seems like a million dollars in loose change."

"A bag of sand or kitty litter. A 5lb bag of the cheap stuff is fine. Pour it under your tires to get unstuck from mud or snow."

"Oil. Lots and lots of oil. I drive a rotary."

iasip1986 said:
"Registration."

Philip_De_Bowl replied:
"Insurance."

"I keep a couple of old hoodies in my trunk. It never fails that we go out somewhere and it seems nice when we leave the house, but then ends up being chillier than expected. That way I’m not cold and miserable.

They’ve also come in handy to warm up/dry off when unexpected rain pops up."

"I keep a baseball bat. Makes me feel safe."

"Breath mints."

"Shoes. You never know when you have to run."

"A wooden stake.

It's been in every car I've ever owned, in the little flap behind the passenger seat (so I can reach it). I whittled it in college, sitting in my car bored between classes. Obviously, this was before smart phones.

I used to keep it there because I thought it was funny to be prepared for vampires, but it's become kind of a totem that I transfer to every new car."

"Hot sauce. Get a small bottle of Franks and keep it in the center console. Get a bland sandwich from the drive-thru? Hot sauce. Not enough sauce with your chicken nuggets? Hot sauce."

"Deodorant."

"Scissors to cut the seatbelt in case you ever get trapped."

"Q-tips. When you get that inner ear itch and wish you had one, you'll thank me."