I've never been to one where fabric was brought, except organized into a kit to make the "workshop" project.
I have seen them sell books, patterns, occasionally notions if they pertained to what the "project" was.
Maybe some of your precuts. Definately hand out cards of your website, maybe offer them a "code" for a small discount on purchases(within a certain date or timeframe) that you only offer to the ladies(or gentlemen) at the guild.