Last year I posted on Hiking Safely, and after posting, I spent a month and a half working in the White Mountains with my brother as crew in a mountaintop hostel dealing with LOTS of small emergencies, (plus a few big ones) many of them brought on by simple lack of preparedness. This has applied even MORE to my Wilderness Search and Rescue work. It's dangerous out there, people! I don't just mean the bears (BEARS!) moose, rock slides, etc. I'm talking about darkness, cool temps, drizzle, all the things you don't think of when you think "hazards".
1. Pack an Emergency Bivy. Emergency blankets suck. I've used them on car accident victims, and they blow off in even a light breeze. Invest in a "bivy sack" for emergencies. They're under 20 bucks, and TOTALLY worth it. It's basically a metallic sleeping bag-style sack that's orange with reflective stripes. If you were to be caught out or hurt you could climb in WITH all your gear, and survive the night, or wait for rescue. REALLY WORTH IT.
2. LOOK AT THE MAP BEFORE YOU GO. The main reason people call for rescue in MY favorite mountains (the Whites) is that they overestimate their abilities, and get "exhausted" before they make it back to the trailhead. If you've never done more than a mile or two, DON'T plan on going THREE miles to the pretty waterfall without remembering that it's ALSO three miles BACK. If you DO call for rescue, (and can GET a cell signal) it could be some hours before people can get to you. Rescuers are volunteer, and a crew may have to get out of work, pack their gear, and hike in from quite a distance, depending on where you are. Therefore, MAKE SURE YOU CAN SPEND A NIGHT OUTSIDE. If you're not critically hurt (fell off a rock wall climbing, stomped on by a moose, fell in a stream and broke your leg, etc) you should be prepared to spend a solid night outside before you could be rescued. If simple exhaustion is your problem, think about this- IF you could wait overnight, would you THEN have enough energy to hike out? If this is the case, DO IT.
3. TAKE THAT MAP WITH YOU- this will sometimes be ignored (even by me, and ESPECIALLY by my brother), but if you don't REALLY know the territory, have memorized every trail turning and its approximate distance, and feel comfortable getting yourself back out of that area WITHOUT assistance, BRING THE DRATTED MAP!!! Sometimes a trail has a BUNCH of junctions, and without a map its really easy to get turned around. While we're on the subject, LEARN HOW TO READ A TOPOGRAPHIC "topo" MAP!!!!! Those little lines indicate ELEVATION, and are in increments. Someone who can read a topo map is able to summon a mental image of the landscape, simply by looking at those lines, to identify ravines, waterways, ridges, etc. This helps if you get off-trail, and need to know where you are.
4. Backpacker.com has a good list of hiking essentials, but my top gear list would be the following:
NON COTTON clothing (cotton does not insulate when wet, and is heavy)- shorts and teeshirt
-raincoat and pants (dont need to be expensive, but need to keep water out)
-fleece jacket of some sort (the cheap ones work fine)
-iodine tablets (in case you have to be out there a while, to purify water)
-an EMERGENCY BIVY
-headlamp (seriously, dozens of people every year need rescue because "it got dark out"...BRING A LIGHT! Flashlights tend to be heavier, and you need to hold them, which can screw up your balance. Headlamps can be gotten CHEAP, and are worth it. I carry TWO.
-hat and gloves
-plenty of water
that's the minimum. hike in peace, and enjoy the outdoors!!!
Addendum: I carry a bit more than this, just based on my personal experiences-
A. I carry a very light first aid kit, even when I'm not on a rescue, with benedryl tabs, an epi pen, advil, immodium, pepto, a few bandaids, steri strips, and purell. This is because i can improvise most dressings with clothing, but it's internal complaints that will prevent your walking out of the wilderness. Pain meds, and ESPECIALLY stomach/intestinal meds, will give you the wherewithal to get yourself out.
B. In cooler seasons I carry a softshell, and wear softshell pants. Softshell fabric is water resistant (very) but super light and breathable. It's not necessarily cheap (unless, like me, you religiously keep track of clearance deals), but it's worth its weight in gold. You will be dry, not sweaty, warm (but not hot), and insanely comfortable, because most of these fabrics stretch nicely.
C. WOOL. This is my latest revelation. The new technical marino wools (Smartwool, Ibex, Icebreaker, etc) are, quite simply, the Best Things Ever. They do not stink, even if you are a large man and wear the same shirt for a week. They do not get out of shape. They maintain insulation in driving rain, and you can wash them in the washing machine. I am a complete convert. i even wear wool camisoles or long sleeve shirts under my scrubs. i SLEEP in wool yoga pants in winter. It's not itchy, it's AMAZING- like silk, but durable. If you make one "expensive" clothing purchase for the outdoors, skip the fancy raincoat and go straight for the wool longjohns. Plus, lots of it look PRETTY, and I've gone on DATES wearing my wool shirts, and have gotten nothing but compliments.