"Maybe we can make this thread more productive: what specific spiritual techniques would you recommend to achieve calmness, clarity, strength, etc., in a survival situation?"

Definitely meditation.
Which means focused control of breathing, as a way of calming nervous responses in the body and so calming the mind. This type of meditation can be practiced by anyone. It is often viewed as a "spiritual" pursuit, but in its most basic form it is not affiliated with any one religion or philosophy.

HOWEVER - in order to use this technique effectively you would need to practice it regularly. For example - take a good tai chi class, and do it at least a couple of times a week. If you can make your meditative skills strong, you have a much better chance of calming yourself in a high-adrenaline situation.

Oddly enough, my own experience is that very few Christians practice serious meditation. I am talking about the kind of "Eastern meditation" that involves clearing the mind and focusing on breathing. The same may apply to many Muslims as well. These large religions do teach people to pray, but there is no instruction about linking the mind with the physical body. In fact, followers of both religions may actually discourage "eastern meditation" because they see it as a threat against their own beliefs. Practically speaking, this may be an explanation as to why someone on this thread observed that there "didn't seem to be any difference between people with different faiths" when they are in emergency situations. If meditation is not trained ... it is not available as a skill when needed.

cheers,
Pete2