One bag in the trunk handles most of what goes wrong

It's 9:40 on a Tuesday. Practice ran late, the lot is nearly empty, and your car makes a clicking noise and nothing else.

A dead battery isn't a disaster. It only becomes one if you've got nothing in the trunk and nobody picking up the phone. The fix is a small bag, about twenty minutes of practice, and a little knowing what you're doing.

The one

A small duffel or a lidded bin that lives in the trunk, built around four items:

• A portable lithium jump starter. Look for one the maker lists as rated for your engine size and fuel type, gas or diesel. It should have clamps with reverse-polarity protection and a charge indicator. A USB port that charges your phone is a bonus.
• A 12-volt tire inflator. It plugs into your car's outlet and should have a built-in gauge. Check that the cord and hose will reach the tire farthest from the outlet. Measure your car, don't guess.
• A tire pressure gauge. Pencil style or digital. Pick the one you can read at a glance.
• An LED flashlight or headlamp. A headlamp keeps both hands free, which matters when you're holding a phone and a lug wrench in the dark.

Around those, add work gloves, a rag, a basic first aid kit, reflective triangles or LED flares, a phone charging cable and a bottle of water.

In the glovebox, keep your insurance card, registration, and a card with your parents' phone numbers written out. Phones die too.

Why this one

A dead battery, a low tire and no light are about as ordinary as new-driver trouble gets. This bag handles all three without a tow truck.

A jump pack beats jumper cables for one reason. You don't need a second car, and you don't need to flag down a stranger and park nose to nose in the dark. You clip it on, follow the instructions, and go.

The inflator and gauge do quieter work. Your correct tire pressure isn't the big number on the tire's sidewall. That's the tire's maximum. The right number is on the sticker inside the driver's door jamb. Check all four tires about once a month, when the car's been sitting, and a slow leak gets caught before it strands you.

The bag is only half of it. The other half is knowing the car it rides in. One weekend afternoon, sit in the driveway with a parent or another adult who knows cars and do this:

1. Open the owner's manual to the pages on jump-starting and changing a tire.
2. Find the spare, the jack and the lug wrench.
3. If your wheels have locking lug nuts, find the key. Everyone forgets this one until they need it.
4. Loosen one lug nut by hand, just to feel how tight it is, then tighten it back.
5. Read the jump starter's instructions out loud, then connect it with a parent watching, even if the car's running fine.

That's the part nobody wants to do, and it's the part that makes you the guy who stays calm. It's also the same habit behind reliable men being built at fifteen, not thirty. You prepare before you need it.

And the kit isn't only yours. Eventually it's your buddy's car in that parking lot, or a neighbor's, or your mom's. Be ready for that. Then do the old-school part. If you use the first aid kit, restock it that week. If you borrow the jump pack to help somebody, charge it before it goes back in the trunk. Leave it better than you found it.

What to skip

• The 100-plus-piece "emergency kit" in a bright bag. A lot of it is filler, and the tools tend to be flimsy. Buy the four things that matter instead.
• Big peak-amp numbers on jump starters. They're a marketing figure. Go by the engine sizes and fuel types the maker lists for that exact pack.
• Thin, cheap jumper cables. If you go with cables, a lower gauge number means thicker wire, and thicker is better. Longer is easier to use too.
• Shop-size air compressors. You don't need a tank. You need the plug-in kind that fits in a corner of the trunk.
• Multi-function "survival" gadgets. If it has a hundred tools, it probably does none of them well.
• Tire plug kits, until someone has taught you. They're a real tool, but a half-learned repair is how a small problem gets bigger. Learn it in a driveway first.

If your situation is different

You live where it snows. Add an ice scraper, a small shovel, a blanket, and something for traction like sand or cat litter. Keep a warm hat and gloves in the bag from fall through spring.

Your car has no spare tire. Some don't. Check the trunk floor. If it's got a sealant kit or nothing, the inflator matters even more, and you should ask a parent whether your family's insurance or a membership already includes roadside help. Put that number in the glovebox.

Your car has a big engine or runs on diesel. The jump starter's listed rating matters much more. Read the maker's chart against your engine, don't assume one size covers everything.

Money's tight. Start with a gauge and a flashlight. They're cheap and they do real work. Then ask whether the household already owns jumper cables or an inflator before you buy new. If you're paying for it yourself, buy the jump starter first and add the rest as you can.

Before you buy

• Read your owner's manual for engine size, fuel type, tire pressure and where the jack lives.
• Check the jump starter's spec sheet, from the maker, to confirm it covers your engine.
• Test that your 12-volt outlet works, and whether it only works with the key on.
• Measure from the outlet to your farthest tire against the inflator's listed cord and hose.
• Read the actual warranty document. Look at how long it runs, what voids it, who pays shipping and whether you have to register the product.
• Read the one-year-later owner reviews and look for complaints about the clamps or a pack that won't hold a charge.
• Ask a parent what you already own before you buy it twice.
• Check the current price.