Transporting non-food items, such as toys, to the food or water bowl is a common behavior seen in indoor cats. The reason why they do this isn’t clear, although several explanations have been suggested. Cats often put their toys away in a “safe” place after playing with them, and cats look upon their food area as a secure part of their territory. This behavior is similar to cats in the wild who often take their prey back to their nest area to hide it from potential predators. Your cat simply might be storing his toy in a secure area to be played with later. (When my cat, Mittens, is finished playing with her fuzzy mice, she likes to store them behind a large flowerpot in the corner of my living room.)
Another possible explanation is that this is a manifestation of gathering/collecting behavior. For example, cats will transport the toy to the water bowl in the same way that a queen will return wandering kittens back to the nest, or move kittens from one place to another by the nape of the neck.
