REI has put an article updating the classic 10 essentials to a more up to date version, along with discussion of the rationale for the choices. http://www.rei.com/gearmail/gm0321_3/cm?cm_ven=email&cm_cat=gm&cm_pla=na&cm_ite=03_21_gm
As you can see from the two lists below, there isn't really much difference between the 1930s version compiled by the Seattle Mountaineers and reproduced in every edition of the "bible" of the outdoors, MFOTH (Mountaineering: Freedom of the Hills, for those who do not yet have one in a prominent place on their bookshelves) and the 2007-8 version. The person who wrote the article for REI, T. D. Wood, relied heavily on the current editors of MFOTH.
As I have posted here before, and explicitly stated by Wood, the 10 should form the foundation of your pack, and you should tailor what you carry to where you are going and the most likely worst conditions to be encountered (an accident involving your party or another you encounter, or for some reason becoming benighted). It should be clear that what you carry for #3 Insulation, for example, will be different in the summer in Death Valley, in the winter in Baxter State Park, or in the summer in Rocky Mountain National Park, or in the places of my most recent extended trips, Antarctica's Vinson Massif or the Serengeti Plains in Africa. On Vinson, you don't need to prepare for malarial mosquitos or 90F/90%RH, but you do need insulated clothing good to -40 or lower and 70 knot winds, where on the Serengeti, you don't need the -40 clothing, but you should include clothing that repels the mosquitos (there are permethrin soaks for the clothes you have) and you need clothing that will keep you cool during the sunlit hours.
I did get a chuckle out of the terminology, though. In keeping with our High Tech era, it is now the huge leap forward to a Systems Approach (I spent most of the industry part of my working life as a Systems Analyst and Systems Designer).
Updated Ten Essential "Systems"
1. Navigation
2. Sun protection
3. Insulation (extra clothing)
4. Illumination
5. First-aid supplies
6. Fire
7. Repair kit and tools
8. Nutrition (extra food)
9. Hydration (extra water)
10. Emergency shelter
Classic Ten Essentials
1. Map
2. Compass
3. Sunglasses and sunscreen
4. Extra clothing
5. Headlamp/flashlight
6. First-aid supplies
7. Firestarter
8. Matches
9. Knife
10. Extra food
