No secret sauce here. The member hosting provider we use, Wild Apricot, does not have the functionality to allow members to cancel themselves from a waitlist, only an admin can do that. I have no idea of why this function could not be possible and have requested that this feature be added quite some time ago (as have other users of Wild Apricot) but so far they have not modified the software to allow this feature. So, if you need to cancel off of a waitlist, notify the trip organizer for that event and they can have this done.