Send your volunteers a text or give them a call. Confirm the details, point them to the resources (listed above), and remind them to bring a charged smartphone or tablet with internet access, water and to dress for the weather.
Consider asking a few volunteers to arrive early on the day to help set up and greet people, or take on other additional roles, like someone to take photos or to help with tallying the numbers at the end.
Need support? Get in touch with your ACF organiser if you encounter any problems or have questions, or ask other volunteers on Slack.