Salt.
Salt is essential and never goes bad.
I find stuff like beans, rice, powdered milk, spices, nuts, keep almost indefinitely if stored in the freezer. I use canning jars because with the lids, they are hermetically sealed so freezer burn is much less an issue.
I use used canning lids for this purpose because I don’t like to reuse them for canning but don’t want to throw them out if they can still be used for something.
Other jars I use are jars like spaghetti sauce jars, the ones that are glass and have the metal lids with the built in gasket. That way, I don’t have to buy jars and lids.
...Salt.
Vitamins, and “No Salt” (KCl) for potassium supplement if necessary
yes, I use old canning lids to top off my storage jars, as well if I wash out a jar, I put the old lid on so the jar stays clean and no bugs....