Arable land, antibiotics. The latter would be worth many many times the value of gold in a post-collapse scenario.

food

air

water

sunlight

sex

People are willing to pay for all of these things.

That's the opposite of what chatmasta asked for.

iron, can be made in to plows or swords.

There is a 0% chance that I turn raw iron into a plow or sword. It has _no_ intrinsic value.

If I received iron in trade for some goods/services the _only_ value it would have is as currency.

You could leave a piece in a pot as you're making soup if you are iron deficient. https://en.wikipedia.org/wiki/Lucky_iron_fish

But if I already consume enough dietary iron, then the iron has no value.

How can this be if it is supposed to have intrinsic value?

Either I literally always need to consume more iron or the iron has no intrinsic value.