Have you considered a butterfly or dove release?
You could have a “green” wedding. You could plant a tree. If it can’t stay there, water (from two vessels) a small potted tree and then take it home to plant in your yard. You could give your guests packets of flower seeds.
If a beach ceremony, how about the unity sand and/or blessing shells?
You could have the ceremony and reception on a boat.
If the weather will be hot, you can print your ceremony program on hand fans. Bottles of water can be labeled with your names and wedding date. Just be sure someone is delegated to pick up everything after the ceremony.