Which of the following items is explicitly prohibited on the beach or pier?

The presence of glass on the beach or pier is explicitly prohibited due to safety hazards it poses to visitors. When glass breaks, it can create sharp shards that can lead to serious injuries for beachgoers, pets, and wildlife. The ban on glass is a preventive measure to maintain a safe and enjoyable environment for everyone.

Other materials, like wood, plastic, and cardboard, may also have restrictions or guidelines, but they do not carry the same level of immediate danger to public safety as glass does. For instance, while large pieces of wood can be cumbersome or create obstacles, they are less likely to cause injury in the way broken glass does. Similarly, plastic and cardboard can be important in the context of littering or environmental impacts but are not typically associated with the same kind of immediate physical danger. Thus, the prohibition of glass is primarily focused on safeguarding health and safety on the beach and pier.