What will we use for currency?

Fallout uses bottle caps. Metro uses ammo. What will the world of Project: Us have as currency?

I was thinking raw iron (which you could choose to either spend on goods or forge into weapons and armour), or maybe seeds. What do you think we should use as currency in this post-apocalyptic world?

I'm fairly indifferent for the currency, but the more I think about it, the more I think bartering/trading wasteland junk makes the most sense. Even though I hate the system... It makes the most sense! But that's just my opinion.