The guidelines for what does make a CAS experience are:
It must be one, or more, of creativity, activity or service.
You should be interested in it and expect to enjoy it.
It should provide an opportunity for growth and allow you to develop the IB learner profile.
Normally you would be able to address a CAS learning outcome.
However, there are several things a CAS experience can not be. These include:
It can not be paid work. For example, if you get paid to be a lifeguard, then it is not CAS.
It can not be part of your official IB Diploma Programme study. For example, if you are undertaking Dance as a Group 6 subject, a performance you are using for the IA is not CAS. Likewise, if you are involved in Model United Nations (MUN) as part of your Global Politics IA, then it does not count.