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 Create a session option from scratch (used by this session only) and click OK
  6. Input session option name and price
  7. Select Edit Details
  8. Click Session option type dropdown
  9. Select Create new session option type
  10. Fill in session option type 
  11. On Display type dropdown box, select Pre-checked and required
  12. Save