The Coin Cases holds Coins, the currency of Game Corners. If the player does not have a Coin Case, they cannot obtain Coins, so cannot play any Game Corner games.
In the Generation I, II, and III games, the Coin Case can hold up to 9,999 Coins; in the Generation IV games, the Coin Case can hold up to 50,000 Coins. Any excess Coins the player would receive are lost, and the player is prohibited from purchasing more Coins.
When used from the Bag in the overworld, the Coin Case tells the player how many Coins they have.