For something to be a currency it has to be:
-Widely accepted. Almost everybody would accept that currency. That means, most of the people would find a use in it.
-Can be divided, or be small enough. For example, you can't use livestock as currency.
-Scarce. If it is too easy to get, then nobody would accept it. (think of the ridiculous abundace of meat in game)
-Non-perishable. It has to have the potential to be stocked.
So, other posible currencies that I have thought:
-Salt (it has been used IRL). Can be used to preserve food. That's something that even end-game characters would need to use.
-Batteries. The problem with this is that end-game characters wouldn't find any use in them.
-Bones. Useful for crafting and making broth.
-Cooking oil. Mostly the same reasons as above.
-Gasoline. The problem with this is that a sudden discovery of a gas station wold cause a lot of inflation.
To be fair, though, inflation was a thing with most currencies, even if we might like to think that what we've learned about economics will stick with us through the Cataclysm. Leaving aside inflation, gasoline might be a bit too bulky, and bones a bit too common, though; execute animals or zombies and grab their bones. Salt does remind me that spice (especially pepper) might also be another possibility, though - not essential, thus reducing the need to hoard, but highly valued for its ability to add flavour to otherwise bland, gamey, and/or occasionally nearly-rotten food. It was only a few short centuries ago that a single shipload of pepper sufficed to pay back the backers of Magellan's five-ship expedition that left three years before, and with the world gone to pot, things like pepper and coffee are now cut off from replacement as far as New England is concerned. It might be a bit too scarce, though: a currency that's too scarce simply won't be used by most people since they can't obtain it in the first place.
I like ammunition (which could even have exchange rates based on what gun calibers the local area has in plenty), but I don't think a real singular currency will evolve in the near term - I think that until society finds a stable footing, the economy will remain on a direct barter system, and once a society or multiple societies find stable foundations for recovery, they'll try to create currencies that scavengers can't supplant or undermine (thereby also enhancing their own power over those scavengers). Basically, coinage, either of precious metals, iron, steel, or copper. Possibly even aluminum, though that's probably too ductile; it may be quite common today, but until they can get some large power plants up and running, the Hall-Héroult process is going to cost a prohibitive amount of energy if they want to make more. There's a thought - a Mad Max-style society that goes around and confiscates pop and beer cans for the good of the state and to avoid debasing its currency. Recycle or die, indeed.