The greater co-op community has embraced a tool that can help a food co-op define roles for their directors and managers. It's called Policy Governance. It is a set of boundaries by which a co-op staff and directors can optimize their work together, delineating when and how they stay out of each other's ways and when they could cooperate for maximum effect. It clarifies responsibilities.
The key to policy governance is to focus the board's responsibilities into three areas: setting long term ends (or outcomes) and organizational limits; holding the general manager accountable for organizational performance within those ends and limits; and, creating an active dialog with the member/owners about updating the ends of the organization. Ends policies are supposed to answer the questions: what changes, for which people or need, at what cost?
Since it is not enough just to write policies and hope for the best, the Board checks to make sure that the written policies are being followed in actual practice by receiving Monitoring Reports. These reports generally cover two aspects: forbidden practices and very desirable outcomes. Since we have lots of policies to review, the Board divides up Monitoring Reports so that we review our policies at least once annually.