I recommend gold be included to ensure against low interest rates along with a stagnating economy. But the truth is, any physical asset, even houses if bought cheaply, would serve the same purpose. Gold is just the most compact and fungible physical asset I can think of.
The public library in our small town is not well funded, and as a consequence, there are a lot of old books on its shelves that haven't been replaced in many years. It's a real eye-opener to browse the financial shelves and see all the books written during the stagflation period of the late-1970's. Some of the writers of these books recommend some seemingly outlandish schemes to defeat inflation, like stocking barrels of heating oil in your backyard (the author includes directions for adding stabilizing agents to the barrels), and building a covered platform and buying steel products like girders and sheet steel for long-term storage.
These seem like ridiculous ideas now, but the important point is that they seemed reasonable at the time. In the late 1970's there was inflation as far as the eye could see. Of course, by the time these books were written and published and finally stocked on library shelves it was way too late to take advantage of any of these ideas, but the writers were writing their "wish I hadda done it" stories in light of their current situation.
This writer is suggesting diversification among monetary instruments; money market funds, stocks, and bonds. But he left out the "real" money of final analysis; gold.
Now it's not likely the world will completely devolve into anarchy, but just the same, the value of gold will likely stay relatively constant, while the value of money market funds, bonds, and stocks will always depend on the value of the underlying currency. Who can say how many dollars it will take to buy an ounce of gold down the road a ways?