It is mainly a plant swap. Many folks bring perennials that need dividing or starts of annuals, whatever you have extra and want to share. In the past there have been daylilies, irises, bluebells, jack-in-the-pulpit, tomatoes, sweet potatoes, herbs, lilies, bell flowers ~ you name it. One fall I scored a bunch of Kopper King hibiscus plants so I over-wintered them and brought them to our swap.
We have a potluck, talk a lot and eat too much, swap plants and then talk and eat some more. If there are several people traveling, sometimes there will be a casual get-together on Friday night.