Dying Light 2: 10 Crucial Things It Must Improve

Easily the most nitpicking entry on this list, it should be addressed nonetheless:

There is virtually no reason for an economy to operate on cash during a zombie apocalypse.

In Dying Light 2, the trailer makes it clear that it's been 15 years since the city fell to the zombie plague. That's enough time for all paper money to become most useful as kindling.

One suggestion is to use a bartering system (with potential upgrades acting as perks), where each item is assigned an arbitrary value. When the value of the items you want to sell is within range of the items you want to buy, a transaction is complete. Items change hands, but no defined currency is exchanged, as would likely be the case should a zombie apocalypse actually break out (probably).

Another suggestion to just wholesale copy-paste Metro's bartering system, which used high quality bullets as currency. With ammunition becoming a scarce commodity, it would surely be of great value, as well as creating a market for lower quality bullets that can be used for shooting. Similar to the Metro series, high quality bullets can also be used in a crisis as actual firepower, although doing so would actively deplete your money.

Whichever system is chosen, or a different one altogether, would really help with immersion into a desperate world.