Subscriptions are auto-ship orders that can be as frequent as once a week or as infrequent as every 2 months.
At this time we cannot add one-time products to a subscription, but if you would like to add other items you can simply skip your next delivery by clicking manage subscriptions, and place a normal order for what you need. Your next auto-ship order will process on the date provided.
Keep in mind that subscriptions will automatically cancel if the item you're ordering is out of stock, and you will need to renew your subscription manually.