You need nothing.

Nothing reminds people of there overconsuming, asset accumulating, wasteful ways. It's a black wooden block that sells for a hefty $48, which is kinda steep price for "nothing." But the idea is good. Hopefully, the block will indeed work as a nudge for people to enjoy everything else they already have in their lives rather than becoming a status symbol for a person who owns it (only the limited edition of black blocks was produced, so if you have one, you're already ahead of the pack.)