You are encouraged to take a piece of the Mystery Hole home with you.
Here’s how you do it:
You may also bring items that won’t fit in a container, like a Wishful Finder Stone™, plus a container about the same volume. Taking both down into the Hole, leaving the item, and closing the container will give you a piece of the Hole about that size.
Items made of material that disintegrates may also be interred: by encasing it in concrete, you can bury the hatchet, or anything else you choose. (Wet concrete availability limited).
Anything that will withstand the moisture and pressure of the earth indefinitely is a welcome addition for refilling the Mystery Hole. Some items might break, might not: like small, strong glass vials or hollow ceramics filled with sand.
Plastic is likely to be eaten by bacteria which evolves in the future to take advantage of an abundant food supply, so it’s only an appropriate material when encased in concrete.
Thank you for contributing to a fascinating future mystery.