1.) Invest in a natural monopoly. That's fine, but most of these are highly regulated (e.g., utilities) and limit your returns.
2.) Invest in real estate. This is rent seeking at its finest. Henry George [1] addressed this issue, but his ideas have not been widely implemented (unlike Marx).
3.) Invest in government debt. I'm always surprised that people like Krugman and Piketty never bring this up, but the fastest way to reverse inequality would be to default on the national debt. The debt is just a transfer payment from tax payers to wealthy debt holders. It is almost like Feudalism.
4.) Buy and hold a nonperishable commodity.
Even your example, the housing market crash, is not an example of hording. In fact, it is the opposite. It is the squandering of capital. Piketty might even argue it was a good thing (like WWII) since it reduced inequality. Or at least it did until the government intervened.