If you got your game in the metal box from DEFCON, you may have noticed that shells didn't come in the box. Hopefully you were able to pick up some dice or tokens or something, but really, a roll of pennies, torn squares of paper, really anything can be used as a token. If you have access to a 3D printer, you can even print some shells here from this fancy STL file. You will probably need between 30 and 50 tokens for a game, depending on the number of players.