Business cards / free mini art print - multi-purpose and it makes customers happy
Branding - On signs, packaging, price sheets, etc. Pre-brand bags with stickers if necessary :P
Coupons - for stuff that's sold out, customers can order online. Change this coupon code for different events to track which events are giving you repeat customers.
Prices - Price list in acrylic stands? Price tags on items
Pickup - offer market pickup where people can order ahead and pick up at the market
Payment Methods - Square Reader to accept cards and Apple Pay, cash, and Venmo. Separate phone/tablet to accept payments?
Socials - Sign that says “tag me @blahblah”
Schedule - Events tab on your website
Inventory - Keep everything in bins in case of rain or soak.
Collapsible wagon - for transporting stuff to and from car