Everyone else is so close to what I'd say that you don't need me mucking it up - but I will.

Laurence Gonzales' book. Read it, learn it, live it. Read it well enough so that you can remember the lessons of other survivors, because their strengths were almost always mental. The book has lots of good insights into the psychology of survival, you can read it and be convinced that you have what it takes to survive too.

Know approximately where you are, always. That goes for during air travel as well. Between that and the north star, you'll never be entirely lost, just on extended walkabout.

Have a definite mental picture of your survival, whether it is hours or days or weeks away, and how you will help to make it happen. Don't doubt yourself too much. Keep your focus positive, and on the here and now as much as possible. One day, one moment at a time.

Concentrate on the basics - shelter, warmth (protection from the elements), water, food. Increase the odds of rescue by as many signalling methods as you can devise.

The ability to improvise, and adapt. The ability to change plans when the original plan doesn't work out the way you thought.

The ability to listen to others, as well as to lead, to the best of your ability. The ability to tell others when you don't know what to do, to seek counsel, but the will to act on good advice quickly. The life you save could be your own. I firmly believe that outdoor leadership isn't a matter of bringing every one along with you, power of will is for suckers and dead people; its keeping everyone with you alive, whether they choose to follow you or not.

Know your limitations. Stay within your training, except in moments of extreme danger when the safe path would get you or someone you are with killed.

Make mistakes. Learn from them, and move on.

Always tell a loved one of your plans, and when you will report in.

Keep a PLB by your side, and most often the rest of this won't factor in for too long. Its the best $500-600 you never spent on that fancy sleeping bag or tent instead.