1. Cash
2. Gold
3. Artwork
Along those lines, I've taken to the 21st century version:
1. Bitcoin (of course.)
2. Gold (still strong!)
3. Magic Cards (games are this generation's art.)
That's just me though. How are you all diversifying YOUR holdings?
It's an interesting diversification of course. I'm surprised there's no stocks or bonds in there. Gold is not really an investment although lately (ie, last 10 years) people have used it as such. It's a hedge. Look at the return of gold over the long run (not 10 years), and compare it to basically anything, stocks, bonds, real estate etc, it's basically last in return vs. inflation.
I'm not saying it's not good to hold, I think its great to hold, more than 20% of your holdings, probably not. I don't know enough about artwork or magic card enough to comment on.