In the US you can't really count on companies using iodized salt. For example, among fast food companies as of 2010 [1]:

• Burger King usually uses it

• Subway does not

• McDonald's usually does not

• Taco Bell, Kentucky Fried Chicken, and Panda Express are in the middle.

There's variability from restaurant to restaurant in a given chain because usually minor items like salt, ketchup, etc., are left up to the local franchise owner to buy from a supplier of their choice.

[1] https://www.medscape.com/viewarticle/720930

Which is a problem for people who exclusively eat from McDonald’s, I suppose. Most people use salt at home, though, and salt that you buy in a supermarket is generally iodised.

That logic could be used to add anything to it.

There are a bunch of other nutrients that are commonly added https://en.wikipedia.org/wiki/Salt#Fortified_table_salt

Got anything else that's useful in specific quantities and also doesn't spoil?

Anything helpful should be added to it.