Create a sculpture using whatever objects you can lay your hands on. Have participants work in small groups for a specified period of time to create a sculpture. It’s nice if the groups can have some distance between them.
Having a theme helps to get the creative juices going, something suited to the group and celebration. It could be summer, wildlife, gardens, games, or any ask the group to come up with their own theme. When time is up, go on a gallery tour and have the each group explain their sculpture to the other participants. No prizes needed here - participants are always interested to see what the other groups have been up to.