There are three types of currency in the game: Supplies, Coins, and Bucks.
Supplies are used as currency for the stocking of Products at Businesses. You earn supplies mainly by killing Zombies at Supply Depots, although you can earn a piddly amount by killing them at the Front Gate as well.
Coins allow you to purchase abandoned buildings, which can be turned into either Businesses or Housing, and thus grow your town. Coins are primarily earned through selling Products at Businesses, but you earn small amounts of coins by killing Zombies at Supply Depots or at the Front Gate.
Bucks are used in various special circumstances, such as:
- You want to instantly complete the stocking or selling of a product.
- You want to demolish a building and make it something different.
- You want to change the location of a Supply Depots.
- You want to purchase additional Coins or Supplies.
Bucks are either purchased from the Z-Store for "real" money, or are earned through various special in-game actions, such as the completion of Achievements or rescuing a human being chased by a zombie during a supply run.