A linchpin is that little pin that keeps the wheels from falling off -both in actuality and metaphorically.
Everyone who's at all into being prepared has their pet prep. For some it's all about security. They may become a bit over prepared in the gun department. Of course, if someone comes to shoot you and you don't have a gun, you are drastically under prepared.
For some it's all about their bug out vehicle. There are some amazing ones out there. Anyone who grew up liking cars and trucks will be temped by the quest for the baddest bug out vehicle.
Then there's food. One well know survival blogger is big on 3 years of food storage, as that's what you need before you achieve 5 years of food. I like to eat so having a lot of meals packed away isn't bad. Really nice to have a lot of food when 5 friends and relatives stop in for a 5 year visit. The hope is that they'll move on after eating cracked wheat month after month.
One of my biggies is potable water. Three very uncomfortable days without it and you are dead. So I'm all about having a secure supply and good water filtration.
The list could go on and on, but I won't. Suffice it to say there are lot of important preps and everyone has a favorite for most important. We tend to focus on those we like best.
Consider that there may be something even more important than the stuff you own. Even more important than your knowledge and skills. Adaptability. Things never go down the way we plan or expect.
The guy with a great survival shelter, stocked to the max, may suddenly lose it in a divorce -or a fire. (the divorce is nastier as fire might spare something) You could have the perfect prepper set up, but find yourself thousands of miles away and unable to get home. That's when the ability to quickly assess the situation and adapt to it is crucial.
So if I have to pick a linchpin, it would be adaptability. One never knows what the universe might deliver.
A buddy of mine says he isn't too sure if there is a god, but feels certain that there must be a devil. There must be a powerful supernatural force against him as all the crap that has come his way is far outside random chance. He should be grateful. The guy's gotten really good at rolling with the punches. Practice, practice, practice.
-Sixbears