Coins are items found when opening Chests or killing other players, creatures and crates. Coins serve as currency in the game, which you can use to purchase weapons, hats, and shields. Most commonly, players drop a value of 1-3 coins, but you will more often receive 3 coins from those who have more bones, and/or are higher up in the In-Game Leaderboard, than others. There are 3 types of coins, each with a separate value.
Players are only allowed to collect 1200 gold a week. The gold cap goes down by 300 every day, so in 96 hours you can farm 1200 gold again.
The Gold Coin is worth 3 coins and is the most rare. It usually only drops from high ranking players, or from Chests. Trading with the gold stalls will give you one gold coin. Gold stalls have been removed from the game instead you can get coins from creatures, crates and players.
There is a rare chance that a gold coin will appear in the fort storage when two storages are empty for a period of time. Gold coin and Armor set is the only two items that can be keep in inventory for once, due to the fact that coins and armor sets are consumable-type items and inspire as soon as players pick it up from the battlefield, once thrown.
The Silver Coin is worth 2 coins and is more common than the Gold Coin, but more rare than the Copper Coin. You may come across it when killing average players and creatures however it is the most common coin when opening Chests. Breakable Chests have been removed from the game as of the Winter Survival update.
You can see your coins in game at the bottom right hand corner or at the top of the menu screen.