Ammunition was used extensively as currency in my last T2K campaign, at least by the PCs. They'd trade calibers they little or no use for to obtain either ammo they could use, or other goods such as decent quality food.
This wasn't quite as standardised as in Metro 2033, mind, but at least in areas where ammunition was still to be had, I can see it making a very useful "currency" of sorts.
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 "It is better to be feared than loved" - Nicolo Machiavelli
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