{May, 2006 Update: Click here for some new "wrinkles" on this subject!}
It's interesting how this has switched from wrinkles to planning your packing.
I have a list but I don't have to start it from scratch. I have a list saved in MS Word covering just about any possible contingency, type of weather, etc. I print it out and first I go through it crossing out everything I know I won't need for this trip. Then I'll write next to it a number. For example, if it's a 5 day trip in warm weather, I'll write in 5 next to t-shirts. This makes things easy to I rarely forget anything important.
Bob...here's a hint on the sunscreen. Basic things like that are always in my trunk so I have 'em when I need 'em, even if going on a day jaunt around town.
Like Mark, I keep some items always in my car for just in case. Except on rare occasions, the only passenger that ever rides in the backseat is my dog. And that's only when someone rides shotgun stealing her favorite away from her. :-) So, on the floor behind the passenger seat, I have a tote with a rain jacket, hat, gloves, a fleece blanket, a Totes-brand backpack because it's lightweight and zips into something about the size of 2 decks of cards, and one of those small camping pillows that stuffs small in its own little drawstring bag.
In another tote bag behind the driver's seat, I have an atlas, a couple of more detailed local maps, a good guidebook particular to my state, a starmap, and the following in case I'm in a situation where I'm forced to leave my dog in the car when it's really warmer outside than I'd like to leave her there (and then I'm very quick): windshield sunscreen, sunscreens for side windows that have suction cups to hold them in place, and a little, folding, battery-operated fan.
In glove boxes and dooor pockets: backpacker-size first aid kit, individual packets of handi-wipes and Shout (I'm always spilling something), travel-size hand sanitizer, dental stuff (toothbrush, toothpaste, floss), a couple of lighters and some matches (you never know if you might need a fire, right?), GPS, flashlight, Leatherman, headlamp, extra small pocket knife, 12v battery recharger with extra rechargeable batteries, FRS radios, my old prescription glasses in case I lose or break my current pair, tape, small pair of scissors, small sewing kit, dog treats, scissors, pen/paper, tire gauge, and probably a few other odds and ends I'm forgetting right now.
I always have a towel with me because I have a beach towel in my car's colors tucked in to cover the bottom of the backseat for when the dog ends up back there. Sure, it might get a tad dirty and have dog hair on it (I do take it out and wash it once in awhile), but at least I have a towel if needed. And I also have another blanket because I have one of those flannel blankets backed with vinyl that I put on my passenger seat, vinyl side up, for the dog to sit on when she's riding shotgun. It makes a good ground cloth, if needed, in addition to being a really warm, lightweight blanket.
Not done yet....
In my trunk, in one of those trunk organizers, I have a small lantern that telescopes into itself with extra batteries, duct tape, a couple of 24-hour/multi-wick candles that you can use for a bit of heat and even some rudimentary cooking, about 5-6 protein bars, a couple of those new pouches of tuna, jerky, several packets of cup-a-soup and cocoa (in case I'm ever stranded, starving and need to use those 24-hour candles to cook with), an small aluminum "sierra" cup to heat water in, a fanny pack with 2 side pockets to hold 16 oz water bottles, 2-16 oz. water bottles with water in them and a 1 litre bottle of water, a cloth/vinyl folding dog bowl so she can get her water regularly, a a roll of toilet paper, a half-used roll of paper towels (so it's not quite so bulky), sunscreen, bug spray, several glow sticks, can opener, deck of cards, teeny travel-size chess and backgammon games, a small bottle of quick-shine car polish and a microfiber towel to clean off bird poop ASAP (I'm kinda particular about my car and don't want the paint to etch), and the usual car staff: folding, emergency triangle, a couple of flares, some basic tools, jumper cables, rope, fix-a-flat).
Not done yet....
In something called a saddlebag which is a storage unit a couple inches thick that is connected to the underside of the hatch-cover in my trunk, I have my car's manual, a cool kit particular to my car with extra fuses and light bulbs, a small stuff-a-kite that has it's own little stuff sack (for fun on the beach), and a stuffsack with some of the 10 essentials for hiking (the rest are in other places in my car and can be added, if needed: compass, waterproof matches, whistle, reflector, 2 of those foil-type reflective "space" blankets, 2 ponchos, flexible reflective mirrow for signaling, and a small paperback book called "How to Survive in the Woods" with tons of helpful hints if stranded somewhere like how to build an emergency shelter, etc.
My husband gives me a bad time for carrying so much but I love it. I feel like I'm ready for anything.
My sleeping bag, sleeping pad, tent, medium-sized folding vinyl cooler, and telescoping camping chair are in a medium-sized duffle bag ready to toss in the car. My backpacker's stove, fuel, cooking set, cooking/eating utensils, pot scrubber/biodegradable backpacking-type dish soap, some basic spices, a small plastic cutting board, folding knife, and some restaurant-type individual packets of ketchup, mayo, and mustard is in a small duffle bag ready to toss in the car.
And, like any good traveller, I keep my grooming kit with small travel-sized bottles stocked and ready to go, including make-up.
So, really, getting ready for a trip is just throwing the 2 duffle bags descibed above and my grooming kit in the car, adding the clothes and food, and my little 12-volt cooler and I'm ready to hit the road. As long as my clothes are clean, I can be ready to go in about 30-minutes tops.
Oh....and my bed pillow. I always sleep best with my regular pillow. :-)