Cat litter
Having a cat means having a litter box. Even if the cat is mostly an outdoor cat there will be times when the weather is inclement and they will need a place indoors to use as a bathroom. Cat litter provides a texture similar to what they would use naturally.
Sometimes a cat will spray or defecate outside the litter box. This is unfortunately due to a mistake made by the owner, such as an unclean cat box or a strange litter that the cat is not comfortable with. In nature cats use sand or gravel-like textures so that the waste can be easily buried.
Cats are very hygienic creatures and they prefer one or two clean, dedicated bathrooms. Their noses are very sensitive- much more than humans- and if the cat litter is dirty or the box is too full they will often go right outside the box. Keeping a box clean and full of fresh litter will prevent unwanted behaviors.