Bunch of questions, would appreciate some insight:
Does the proportion of sodium to other stuff like magnesium/potassium/calcium/etc. matter? Is 86% sodium better/worse/the same as 99.8%?
If the package doesn’t specify what else is in it besides sodium (e.g. 95% sodium, remaining 5% not specified) is that a bad sign?
Is everything aside from the sodium so nutritionally insignificant it’s not worth consideration (aside from possibly affecting taste?)
Anything in particular to avoid? (how the salt was processed, certain chemicals, etc.)
> 1) Does the proportion of sodium to other stuff like magnesium/potassium/calcium/etc. matter?
Yes and no.
No-part: Think about it this way: The WHO for example recommends consuming less than 5g of salt per day. This is a small amount already and now add to this the 0.x% of micronutrients you can find in there, the amounts become negligible. You´re much better off simply eating a piece of fruit or some vegetable
Yes-part:There are some exceptions: Iodine for example is needed in so little amounts by your body that having iodine added to your salt actually helps you reach the recommended amounts, even when consuming so little amounts of salt. But you have to keep in mind that for iodine the recommendation is somewhere around 50 micrograms/day, whereas magnesium is in the triple-digit milligram/day and calcium even is in the gram/day category.
> 2) If the package doesn’t specify what else is in it besides sodium (e.g. 95% sodium, remaining 5% not specified) is that a bad sign?
No. It´s normal for salt to not be 100% sodium-chloride. There might be some other salts and partially some water in there. Nothing to worry about. Due to regulations (depending on where you live) companies don´t have to declare everything that is in certain products if, for example, the amount is very small.
> 3) Is everything aside from the sodium so nutritionally insignificant it’s not worth consideration (aside from possibly affecting taste?)
If you mean that the amounts found in salt in combination with the amount of salt that should be consumed makes them insignificant, then yes, you´re absolutely correct.
> 4) Anything in particular to avoid? (how the salt was processed, certain chemicals, etc.)
If you´re healthy adult, you don´t have to worry about anything added to salt. Depending on your diet and the region you live in, you can consider buying salt that is fortified with iodine, folic acid, and/or fluorine. These are micros that are needed in so little amounts by your body that fortified salt can actually help you reach your recommended intakes.
In Germany, for example, it´s recommended to at least get salt with iodine and probably fluor (and mostly also folic acid), since we don´t tend to get enough of those from our normal diet.
And pro tip: Salt is salt. If you want to spend money on more expansive salt, go for sea salt. The size of the grain makes the difference. Everything else is just a cash grab.
Edit: Also don’t worry about people saying that fluorine or iodine is poisonous and should be avoided. These are super essential nutrients and we tend to have problems consuming enough with our diets. Also, fluoride in toothpaste is a great way to help reach your recommendation and it’s also really good for your teeth.