Session options are not required by default, but the requirement of purchase can be made. 

To make session option required:
  1. From Home page, click Setup under desired season
  2. Click Sessions 
  3. Click on session name
  4. Select Add a session option under Session Options header
  5. Select Edit Details
  6. Click Session option type dropdown
  7. Select Create new session option
  8. On Display type dropdown box, select Pre-checked and required
  9. Save