Things like gold are asset preservers.
The idea behind buying gold is to hold assets against inflation and loss of value. It does not typically increase in real value. That is, an ounce of gold will, in general, buy the same things 100 years ago, or 100 years from now, that it buys today. I don't consider it an "investment" as such in that it creates no new wealth.
Other commodities have the potential of increasing in real value, like artwork or things like that, but you have to be a very skilled person in the field to consistently buy low and sell high.