Hi Elizabeth. Thanks for contating CTB.
I don't know much about food policy councils per se, so I spent some time on the internet before responding to your question. The article I liked best was:
www.markwinne.com/wp-content/uploads/2012/09/FPC-manual.pdf, specifically chapter 6. It doesn't offer best practices, but does suggest a number of very practical ideas.
Within CTB, please click on our Learn A Skill graphic and then on Table of Contents. Go down to chapters 36 through 39 for our evaluation recommendations. In addition, look through Related Toolkit 12 for specific guidance on evaluation process (which best begins during the planning stages of the initiative).
You might also take a quick look at a Community Story on the Helena, MT community gardens initiative (Click on connect With Others, and then on Community Stories) That article is brief, but you might consider contacting them for evaluation advice.
I hope this response is helpful. You have opportunity to design a good evaluation process of your own if there are not yet any best practices specific to food policy council evaluation.