From the time I joined the Army I was taught to carry the essentials at all times on my body:

Fire starting

Signaling

Shelter construction

Water procurement

This amounts to a whistle, light (I have the Photon Freedom or a military issue strobe which uses AA batteries) or orange signal panel (I have a very small nylon one from an aviator survival kit), water purification tablets (I now use the Micropur from Katadyn), parachute cord.

I was also taught to carry things in order of priority and possibility of being lost (line 1, line 2 and line 3).
Line 1: Carry on your body what you need to survive (in you pockets or on you belt).
Line 2: Carry on you Web gear (for civilian clothing a fanny pack, photo vest or fishing vest)what you need to fight.
Line 3: Carry in you back pack everything else (mission gear, comfort items and additional supplies).

We also had to take into consideration "the naked man syndrome". If you are captured (in which case they take everything, including your clothes) or lose everything in an airplane crash or have to shed everything to prevent drowning your brain is your most important survival tool. you have to learn how to do everything with nothing. Shelter, fire, water and signaling. This is the importance of primitive technology.

I have tons of gear which I carry even around town which my wife finds amusing (until I actually used it in front of her) and the airports are always questioning the stuff at security checkpoints. I always have the Ritter pocket survival pack (minus the razor blade) at a minimum. Foreign law enforcement has found it interesting as well. While in the Army I did use my survival gear on several occasions, not in a survival school, and will never be caught with the stuff in my pockets.