[internaut]

This one will depend on your geographical region.

I believe if you wanted to really hedge against the kind of scenarios that can render stock markets themselves worthless you would own a means of reliably producing electricity.

It doesn't need to be that much. You can build a small hydro planet for as little as 50k. It requires little maintenance and will last a hundred years (they are very efficient but uncomplicated machines). It is something your grandchildren would benefit from.

If you're interested check out Micro Hydro Design by Adam Harvey.