A Basic Tool Kit for Car Owners

Most roadside trouble comes down to a tire, a dead battery or a light you cannot see well enough to deal with. The list below covers those, split by where each item lives, and none of it requires mechanical training to use.

Check what your car already carries before buying anything. Many newer models have no spare at all, just a can of sealant and a small inflator under the trunk floor, and the owner's manual will tell you which you have.

Keep in the car

Tire pressure gauge. Inflate to the number on the sticker inside the driver's door jamb (or in the manual), not the figure molded into the tire sidewall. The sidewall number is the tire's maximum, and running at it reduces grip, makes the ride harsher and wears the center of the tread. Check when the tires are cold, before driving.
12-volt portable inflator. Plugs into the power outlet and brings a soft tire back to pressure so you can reach a shop. Look for one with an auto-shutoff at a set pressure.
Spare, jack and lug wrench, checked. Find them now, in daylight. Check the spare's pressure twice a year; compact spares often need around 60 psi, which is printed on the tire itself, and they are only meant for short distances at reduced speed.
Flashlight or headlamp. A headlamp leaves both hands for the jack.
Reflective warning triangles. Set them well behind the car on the same side of the road. They are more visible from a distance than hazard lights alone.
Work gloves and a few rags. Wheel nuts and battery terminals are dirty, and gloves protect your hands from sharp edges under the car.
Portable jump starter. Works without a second car; keep it charged every few months (the battery article covers how to use one safely).
Small first aid kit. Adhesive bandages, gauze, tape and antiseptic wipes cover most minor cuts from roadside work.
Owner's manual and a card with key details. Write down your tire size, roadside assistance number and insurer's claims line, in case your phone is dead.

Keep in the garage

Tread depth gauge. Most US states treat 2/32 of an inch as the legal minimum, but wet-road grip drops well before that. Many tire makers suggest replacing at around 4/32. Measure in the center and both edges of each tire; uneven wear points to an alignment or pressure problem.
Torque wrench. Lug nuts have a specified tightness, listed in the owner's manual. Too loose and a wheel can work its way off; too tight and you can stretch the studs or warp a brake rotor. Recheck the torque after the first 50 to 100 miles on a newly mounted wheel.
Breaker bar or cross wrench. More leverage than the wrench that came with the car, which helps with nuts tightened by an impact gun at the shop.
Floor jack, jack stands and wheel chocks. Never put any part of your body under a car held up only by a jack. Lower it onto rated stands placed at the lift points shown in the manual, and chock the wheels that stay on the ground.
Basic socket and screwdriver set. Metric sockets from 8 mm to 19 mm cover most battery terminals, trim clips and covers on modern cars.
OBD-II code reader. Every car sold in the US from the 1996 model year has the diagnostic port, usually under the dashboard. A basic reader shows the code behind a check-engine light so you know whether it is a loose gas cap or something a mechanic should see soon. A flashing check-engine light means stop driving and get it looked at.
Battery terminal brush. White or green crust on the terminals can stop a car from starting. Disconnect the negative cable first, clean, and reconnect it last.
Funnel and a roll of shop towels. For topping up washer fluid or coolant without spilling it onto hot parts. Only open the coolant reservoir when the engine is cold.

Worth it if you drive in snow

Snow brush with an ice scraper. Clear the roof as well as the windows. Snow left on the roof slides onto the windshield when you brake.
Compact shovel. For digging out the tires and clearing the exhaust pipe before you sit in a stuck car with the engine running.
Traction aid. A small bag of sand or non-clumping cat litter, or a pair of traction mats, gives a spinning tire something to grip.
Winter washer fluid. Choose one rated well below your usual low temperatures; summer fluid can freeze on the glass.
Blanket and a spare pair of gloves. If you are stranded, these keep you warm without running the engine for long stretches.

Put the in-car items in a single bag or trunk organizer that stays in one spot, and look through it each time you change the clocks: recharge the jump starter and the headlamp, check the spare's pressure, and replace anything used from the first aid kit.