Here is a great little 2-player betting game that you can play with 12 coins and a twelve-sided die (a.k.a. a d12). We call it: d12 Coins.
Have each player bring 6 coins of equal value to the table. Place all 12 coins tails-side up in a row and number them 1 through 12. Each player chooses "evens" or "odds" for the game. Choose a player to start.
Playing the Game:
On their turn each player rolls the d12 and turns over the coin of the corresponding number. If they roll their own number (i.e. the evens player rolls an even number), then they can opt to not turn over the coin. When a player has all of their coins heads-side up (all of the even-numbered coins for the evens player or all the odd-numbered coins for the odds player) the game is over. The winning player takes all of the heads-side up coins as their winnings. The other player takes the tails-side up coins.
Enjoy this little game, and be on the lookout for a very expanded version of this game using twelve-sided dice, coins, and more.