Classes are a popular form of additional material for many games, so this is a fair request. For now, to keep the core categories as inclusive as possible, the types of products you’re talking about would fit best in the Supplements category:
That would be a much better fit than Gameplay tools as it describes the content in broad terms more accurately.
We’ll consider other categories or taxonomies that could serve these needs more closely, but for now, using the Supplements category is they best way to label them correctly.