I was told the most important skill or tool for survival is ATTITUDE. Some of what has been said really covers that. Humor, determination, but also acceptance. Those of us who expect something…a bad something.. to a degree are better of because we expect change and loss. So we know sitting around moaning about it will not do anything. You have to accept the new circumstance and do whatever is needed to make do and survive. And try to keep a positive attitude and impart that to those around you. To believe you will get thru.. and keep hope alive ( even tho you know it is possible that it might not happen).
There are so many different circumstances that I do not know a particular skill which is important. You need to know a bit of them all, and be able to make do as Selco suggests. It might be shooting… but it might be gardening.. or hunting… or foraging… or building shelter… or health care.