An erosion bundle is art supplies put outside in January and taken down in April and then an art project made out of the supplies.
You can read more about it here:
This is the art supplies after staying out all winter and coming inside in April. The paper sack has catapillars on it. The flowers are now white and all the supplies now look faded and worn. The slide holder has a green and a pink side and I forgot that when I took the photo.