Cats need their daily routine to be very predictable and consistent. Some kitties, when they feel stressed by a change in their environment, will start performing a behavior like grooming themselves. This is an example of a displacement behavior.
One very important reason for offering your pet nutritional variety is to help prevent food allergies. When the same food containing the same protein is fed day in and day out for months or years, intolerances often develop.
It's helpful to provide your cat with something to climb on, like a multi-level cat tree or tower. At least you'll know he's been stretching, clawing and working his climbing muscles whenever you see him gazing down at you from atop his tree.