Even the best weapons and armor don't mean that an adventure automatically will be a success. What if a steel door is locked? What if the adventurer is lost in the wilderness or a labyrinth? What to do when the light is gone? This is when the equipment comes into play. These items help enormously. Thus this section of the Codex has these items as the topic.
Additionally, everyday-items which are either of use for the adventurer or that can be used for battle (not that this is their intended use!) are found here.