Very good question/point. I consider being physicaly fit very important. You don't have to be able to run marathons, but walking, lifting, pulling ... are all things you will have to doi in a survival situation. If you are dead tired the day after, you still have to do it all over again . So being fit is an asset.

Knowing you limitations is as important. A fit individual who thinks he can do it all and injures/tires himself out will be at the mercy of circumstances as much as the invalid, elderly, etc...