Pine cone bird feeders? Cover them with peanut butter and roll them bird seed. Our kids made them every year and we'd take them out on the nature trail near our school and put them in the trees.
Paper plate masks with "found" treasures.
Pet rocks that they paint and decorate with glitter, feathers, whatever they have handy.
Paper mache puppets. Cover a balloon with paper mache, let dry completely, pop balloon, paint or decorate, make an outfit for it (making a puppet like this is all I remember about being in 2nd grade), put on a puppet show for parents.
You could ask parents of children who participate to contribute cash or goodies to help defray some of the cost of supplies.