1. Open a rapid board, planning view
2. Click on any item in the list of items
3. The "pre-view" of the cliecked item is displayed to the right, but it's not possible to configure what fields to include in this display.

As we have some really important infromation in custom fields (e.g. the actual "user story" text 'As a Player I want to...'), we currently need to open all issues in new tabs anyway during planning - it's sufficient to only use the rapid board planning view.