"I have been invited to serve on the board of a local non-profit with no stipend involved. Do I need to report this?"
If you are an Investigator, this activity should be disclosed for conflict of interest review if it meets the definition of a Significant Personnel Interest. Significant Personal Interests are any managerial, professional, or Fiduciary Position you (or a Family Member) hold in any outside entity, whether or not you or your family is compensated. This can include officer, director, and board positions.