If you would like to have activities not associated with subjects (topics outline) what you can do is the following. Suppose you need 5 subjects. Go to the course settings and set the weeks/topics number to 6. Add all the activities to the 6th subject and then go to the settings again and set the course weeks/topics number to 5. As a result the 6th subject will not be visible but you will still have all the actitivies. You can provide access to the activities either via the Activities block or by creating web-links.
Hope this helps.