oc_filecache is as big as your ownCloud instance. Many files results in big oc_filecache.
oc_activity can be controlled with a parameter in the config.php:
Apps Config.php Parameters :: ownCloud Documentation
(and it needs Cronjob running, see How to empty the oc_activity table?)
oc_file_locks maybe also an issue with Cronjob not running reliable, maybe check Lock files issues - 65K entries in table oc_file_locks
More information about Cronjobs:
Background Jobs :: ownCloud Documentation