Your cat goes to the food bowl often and will never forget the location of the food bowl.
It is possible that your cat is putting toys in the food bowl so they can be easily located later on. Cats love their toys and like to keep their toys where it is easy to account for them.
It is also possible that you cat simply carries toys around the home, and then drops in the food bowl prior to eating. After eating, your cat may or may not want to carry the toy around — hence, toys left in the food bowl!
Another possibility is that your cat may think the toys are prey. Cats may think that their toys (such as fake mice) are prey. Therefore, they are simply putting their hunted food into the food bowl with the rest of the food!
Your cat may be putting his toys in his food dish as a game. This is even more probable if you constantly remove his toys from the bowl. He has trained you to play this game with him. Does your cat play in boxes? Read the Why does my cat like boxes? article for more information.