There are a lot of things that need to be stored away in your basement, store room or whatever you use for long term storage. Basic foods come at the head of the list, I suppose, but things like medicines, medical supplies, cooking supplies, extra clothing, et al go there too. There are books that are essentially lists for self sufficiency planning, and there are lots of pdf. format files on the internet with the same information.
One of the items that usually shows up somewhere near the bottom is common salt. We tend not to think much about that, but it's really a critical commodity for a number of reasons. We need it to stay healthy, so much so that part of a Roman soldiers pay included salt. We get the word "salary" from the practice of issuing Roman troops with small bags of salt for cooking, then the cost was deducted from their pay by the legion paymaster. The Romans didn't waste time on non essential practices.
People need small amounts of iodine in their diet, and the way most of us get it is by using iodized salt. Failure to do so, over a long period of time, can lead to several health issues, the most well known being goiters. There are people, like me, who can't ingest iodized salt because we're allergic to iodine. If you have someone like that in the family or the group, you need to provide salt that has no iodine for their use.
I found that if I waited til winter, when the humidity here is usually about 20% or lower, I could take the salt out to the barn, pour it into plastic bottles, seal them tightly, and that alleviated the issue of hardening.
There are salt blocks of different size, with or without iodine, that you can buy at farmers depots, and sometimes at big box stores.
However, the same blocks make good long term storage salt for people as well. You can put ten large salt blocks down in the basement, and if the times call for it, you just chip off what you need with a chisel, and break it up with a morter and pestel, If you don't have one of those, improvise one, You can buy these large blocks, roughly the size of half a cinder block, either wrapped in plastic or as plain blocks you need to wrap yourself.
There are also small salt blocks, about the size of a brick, if that's easier for you to move or store.
There are a huge number of uses for salt besides flavoring and preserving food. It's cheap (now), but it doesn't exist in quantity naturally anywhere near most of the places people live. People who have read "Alas Babylon" will recall that the community where the story is based had to send a party to an old salt lick when the town ran out of the commodity.
If you do live near a salt lick or by the beach, you might be able to get your own, but for most of us, what we have on "the day" is going to be what we have to get through.
I'd say lay it in while it's cheap.
Univ. of Pennsylvania: Canning and Pickling Salt
University of Missouri: Canning
Morton Salt: Frequently Asked Questions
Morton Salt Meat Curing Frequently Asked Questions.
The Modern Survivalist: 101 uses for : Salt
The Good Survivalist: Preserving Meat with Salt
The Happy Prepper: Uses for Salt
The Survivalist Blog: Top Ten Mistakes of Prepping Newbs