Salt is essential for life and you will be able to meet your salt needs simply by eating the right naturally occurring foods. But the need and want for salt after society breaks down is important for a few different reasons. Salt makes stuff taste better.
You might not want to risk your life for this use of salt but being able to make your day to day foods taste better is something that will go a long way to making living on your own off the land a lot more pleasant. It might be just a frill but living a miserable existence is not conducive to being level headed and rational.
But in addition to just its use as a spice for foods salt has more practical uses that go beyond just making food taste better. Salt can be used to preserve food. Suppose you kill an animal that is too large to consume in one sitting. Salt is a useful tool to have to help preserve that food for later use. It can also be used on hides to help preserve them as well as for using with preservation of foods such as in some methods of pickling.
OK now that we have established a few of the reasons you will want salt, how do you go about getting salt when you are no longer able to run up to the local grocery store and purchase it.
The best method is to get salt straight form the sea. Extraction of Sea Salt
Extraction of salt from plants