BuddyPress.org

All activity action types are stored in an array. Look at the function bp_activity_set_action in bp-activity.php. Components register their activity actions via this function. They then get added to the array $bp->activity->actions.

Now, as far as filtering out the various activity actions, you can either write some custom code, or wait for my BuddyPress Privacy Component as that is one of the services it provides users.

A final note, if a third-party component fails to register any of its activity action types, then they are not added to that array and it becomes much more difficult to filter them.