Some time ago I decided to tally the miles I’ve driven in my entire life, beginning with my first car, a 1971 Toyota Corolla (116,000), progressing through the two J.C. Penney furniture-delivery trucks on which I put, collectively, over 250,000, on to my FJ40 (316,000 and counting), etc. etc. I was not surprised to find the total well over a million miles.

So you can assume I have my driving environment completely sorted by now, right? Nope. I am always finding myself short something I could really use immediately, or if I have it it’s buried in the back cargo area somewhere. During that million miles there's no telling how much time I've wasted faffing about, as the English say. So I decided to make a list.

• High-quality window cleaner: Even if you’re conscientious enough to put window cleaner formula in your vehicle’s washer bottle instead of plain water, it won’t be strong enough to deal with the really impacted bugs you murder at highway speeds. Yet most common household window cleaners contain ammonia, which dries out rubber seals on vehicles and should never be used on windows with aftermarket tint film. Premium cleaners such as Invisible Glass work well and won’t harm tint film. The corollary to this is, keep your wiper blades in good shape. Test them periodically, before you get caught in a downpour and find they chatter uselessly back and forth. 
• Blue shop towels: These aren’t actually the best for cleaning windows (some pros insist newspaper is the best, followed by a microfiber towel for drying), but they have so many other uses that the versatility wins.
• Dial-type tire pressure gauge: Eschew the cheap pencil gauges and do it the professional way. Tires have become so reliable that they’re easy to ignore, but maintaining proper—and consistent—pressure reaps benefits in safety and economy. If you spend more money on a gauge you’re more likely to use it. I’ve found the models from Accu-Gauge to be good for the money.
• Flashlight/headlamp: LED of course. I like models that combine a low, 10 or 15-lumen setting for reading or doing repairs with a serious, over 200-lumen high beam. You can go the lithium route and not have to worry about replacing batteries for a very long time, or take the available-anywhere-on-earth-and-cheap AA approach.  
• Knife/fork/spoon set: This might seem odd, but I’ve frequently found myself buying some snack on the road better eaten with utensils, and having a set easily accessible is nice. I keep a Snow Peak titanium set in the center console. Steel would be fine, but the titanium saves on GVW and enhances fuel economy. Just seeing if you were paying attention.
• First-aid kit: Keep it in the vehicle and don’t cannibalize it for other uses so you find yourself without the basics when you need them.
• Lens cleaner cloth: A detail, but nice to have and more effective than your shirt. Tucked in a little ziplock in the glasses compartment of fancy overhead consoles, or in the registration pocket of the sun visor.
• Hand cleaner/degreaser towlettes: Not the ubiquitous Wet Wipes; I’m talking about those infused with proper degreaser, such as the Fast Orange or Scrubs wipes. You can get them in a bulk dispenser tube or little packets.
• Nitrile gloves: Degreaser towlettes are all well and good, but it’s better not to get greasy in the first place. I keep a couple pairs in the Land Cruiser, 40 or 50 in the Land Rover ;-)
• Work gloves: The newer fabric mechanic’s gloves are okay, but I still prefer leather.
• Mini binoculars: As a naturalist and birder I of course own a de rigueur set of absurdly expensive German-made binoculars, but I keep an inexpensive compact 8 x 20 set from Pentax in the glove box for impromptu observing. If they’re stolen I won’t be tempted to slit my wrists.
• Flares: Either the traditional fire-and-brimstone type or the battery-operated LED versions. Foldable reflective triangles are also suitable.
• Ground tarp: Years ago I bought a military surplus canvas folding stretcher. It’s incredibly stout, has handles up and down the sides, and folds flat. It’s perfect for working under a vehicle. And, of course, it would serve as a stretcher if needed.
• Insulated water bottle: Leave a steel bottle full of water in your parked vehicle in Arizona in summer and it will soon be hot enough to brew coffee. The insulated versions are far better.
• Notebook/pen: Mileage, fuel purchases, fuel economy, restaurants, birds sighted, road conditions—there’s no end to the stuff crammed into my notebook. The Field Notes brand is a superb source for indestructible products.
• Multitool: Despite that 60-pound tool case in the back, I like to have a multitool to grab for quick non-critical fixes or tasks. 
• Ice scraper: Yes, we have these in Arizona.
• Bug-out bag: Actually an article on its own—a day pack stocked with supplies you might want if there is ever a need to precipitously abandon your vehicle. Sign up for Mark Farage’s excellent discourse on this at the Overland Expo.

Any other suggestions? Comment or email me.