Contents are going to vary according to who you're talking to, how much time they spend in the boonies or rural areas, and personal situation. For instance, if you've got a vehicle with not much space for something like this, you might shrink it some.
I drive a extended-cab mid-size pickup that lets me keep a fair bit of stuff in the back. Here's what I have in mine; remember that this is subject to change according to time of year:
- One to two quarts of water. Quantity depends on time of year. If I'm taking a trip in hot weather, I'll bring at least two quarts.
- First-aid kit. Year-round. No, I won't cover everything in it right now.
- Compressor. The kind that plugs into the cigarette lighter. That thing has been handy many times; rarely for me, but a LOT of people have had their slow-leak tire or spare aired-up with it. Not expensive to buy.
- Light axe & Machete. Happily, I have not had to cut my way out of trouble with these; but they've come in very handy both when out in the woods or after storms. The former, clearing a trail a bit or cutting firewood, the latter clearing downed limbs or trees.
- Toolbox. Mine currently contains sidecutters (think large pliers with a wire-cutter on one side), vise-grip pliers, screwdrivers, battery terminal cleaner, sturdy craft knife (folder with replaceable blades), wrench set, and a few odd things that have migrated there. In a separate, smaller box is a socket wrench and both standard and metric sockets, a socket extension, and a 3/8 to 1/4" drive converter.
- Rope. Heavy green paracord, about 20 feet, and another 20-25 feet of 550 cord. The heavy stuff for whatever, the 550 for lighter stuff. Remember that if you need a bunch of light cord/heavy thread, there are seven strings inside the 550 cord that you can pull out to use.
- Note: this is in addition to the pair of cargo tie-down straps I always have packed.
- Spare knife. 'Nuff said.
- Floor jack. This is a small one, because it's easier and faster to haul it out and use it than to take out the small jack that came with the truck, string together the pieces to crank it, and use it. Got it at Harbor Freight with a coupon for $25.
- Folding shovel. . This one is surplus military. It's something I haven't had to use, but it takes up little space, and the possibilities are great.
- Food. Usually this is just a couple of MREs, for just in case. If I were starting a long trip, especially in winter, I'd have more.
- Flashlights. Plural. A small handy one, a big "I can light you up at fifty yards if I need to" one. Check the batteries regularly.
- Tow strap. Rolls up to a small bundle, much lighter and smaller than a same-size chain. Yes, I had to use it to tow someone once, and it worked nicely.
- Breaker bar and impact socket for changing tires. This is a 18" long, 1/2" drive breaker bar and a impact socket to fit my lug nuts. Good any time, but considering some of the joint problems that flare up at times, this makes it a lot easier to break the lug nuts loose, and tighten them down, when I have to deal with a flat.
- Why an impact socket? A standard socket (usually) has 12, sometimes 18 points in it that bear on the corners of the bolt or nut; this makes it easier to get it in place in confined spaces.
- An impact socket is designed and built to be used with something like a air-powered impact wrench; the greater strength is nice, but the big factor is it only has six points and does NOT bear on the corners; if you feel the inside, you'll find the flats aren't; they're convex curves, so the socket bears on the flats of the nut or bolt; makes it damn-near impossible to strip the corners the way a standard socket can. In the case of a lug nut that's been in place a while, this can be a very good thing.
- Web gear. I have this as a general 'get home' item. It's an old British 1958 Pattern web gear set I found on sale at Sportsman's Guide years ago. The pouches of this are where I keep the water, food, a space blanket, a small flashlight, waterproof match holder, and a few other small things. It also has ways to hang other gear on it, and is comfortable to wear.
- Hat. A boonie-type for hot weather; something that'll cover my ears for cold.
- Sleeping bag or a good blanket. These go in during winter, especially if on a trip,
- Other bits & pieces as they seem appropriate for the occasion/season. For instance, a bag or bucket of kitty litter for winter, for dealing with traction problems.
And that's what's in my truck.