Unsubscribe Token for Subscription Reminders
Generally, there's not a way to opt-out of transactional emails, like receipts and reminders.

I found this in the documentation, which states


  Scheduled reminders are still sent to contacts who have opted out of
  bulk emails and those who have selected the privacy option Do not
  email.


It goes on to say


  If you want to exclude contacts who have opted out of bulk emails from
  a scheduled reminder you should: 
  
  1) Find all contacts who have not
  selected the privacy options Do not email or NO BULK EMAIL. 
  
  2) Create
  a smart group from the search results. 
  
  3) Select this smart group as
  the Recipients of the scheduled reminder.