Why is salt important?
You can't live without salt, your body needs it.
Used for food preservation.
Used for tanning hides.
Making food taste good.
There are ways to get salt on your own, but unless you are living in a few select areas then access to salt in a post apocalypse situation is going to be difficult. Initially you task will be immense, but you will be starting from scratch. Let's not add to your burden by forcing you to do task which can easily be put off for years if you will just prepare now.
If you want to learn about how to get your own salt check out this link.
Finding Salt
When buying salt for you stockpile it is important to get the right salt. You do not want to buy iodized salt or any salt that has other ingredients added. These ingredients, such as iodine or anti-caking ingredients can make reduce the shelf life of the salt. Iodized salt for instance has a shelf life of about 5 year.
Where as pure salt such as Kosher salt, himalayan salt, sea salt, Celtic salt, pickling salt can last basically forever. So, you should be good, if you avoid salts with extra ingredients or salts not sold with human consumption suck as animal blocks and rock salt.
How much salt do you need? You can figure you will need 8 pounds per person per year if you are not getting salt from any other outside sources like canned food and others store bought foods. This 8 pounds is what you will need to keep yourself alive for one year. But keep in mind that in a SHTF scenario you will need salt for other purposes such as tanning hides and preserving food. So, factor in 8 times the number of people times how long you want to live!!! Only half joking. And then stockpile more for food preservation and tanning of furs, etc.!
So you bought a bunch of quality salt, great! However you aren't done yet. sSlt is hydrophilic which means it absorbs water out of the atmosphere. Do to this property you will need to store your salt in air tight containers.
The original cardboard containers are not good long term storage containers and worse they will look good on the shelf while inside the salt is a sloppy mess.
If you store your salt in big buckets, then the salt will require very long periods of time to use up due simply to its volume. Each time salt is extracted you introduce fresh air and moisture into that container. You can, however, use a large seal-able bucket to not store salt, but are storing them as a bucket for of salt in their original containers. You only open the bucket a few times to remove the next salt container. However, if possible store in glass anyway just for peace of mind as numerous glass containers are best. When storing in jars avoid metal lids if possible. Salt tends to make metals rust!
Side note tip. Iodine is an essential nutrient for your body, so keep up to 5 years supply and replace the iodized salt as it is used. Always using the oldest salt first.