There are many different challenge coins with different shapes , sizes and colors which are given to the soldier at different occasions like for the appreciation or any time in exchange for the post and given at some specific task. If someone has the unique coin then it means that person has done some valuable task. There is no need to give the challenge coins to every member within the group.
So there are some coins which represent very much serious situations which are the part of the relax tradition. Sometime there is the situation in which these coins are also given just for the challenge the fellow soldier. For example if they're all the soldiers have gone together and one of them has the challenge coin then that person can challenge the other soldiers for producing that coin. And the person is fall to produce the coin then he has to buy the drinks for others and if the challenger is failing for his given challenge then he has to buy the drinks for others.