Commodities 

 Gonna be tricky to carry pork bellies or barrels of oil to the store to buy groceries, but I guess we'll do what we have to do! 😂 

 You laugh now 

 My guess is some kind of crypto. It won't be official but it'll happen anyway.

I used to think gold had an equal shot but the more I thought about it the more I realised it's much much harder for average retailers to accept gold than crypto. 

 Something like the Rentenmark-to-Reichsmark transition seen in Weimar if I had to guess: a currency backed officially by a mix of gold and hard commodities. Maybe crypto ledger technologies will come  in handy to support it.