Some play yards feature a mobile with suspended toys or a detachable baby gym that can also be used with the bassinet mattress on the floor as a separate play mat for tummy time. These are a bonus, as are entertainment centers with music, soothing sounds, and lights. But all will contribute to the price and weight of the yard, and will make it more difficult to pack up the play yard for storage or travel. They usually require C or AA batteries (not included). Toys may not be necessary if you intend to use your play yard as just a portable nursery. But if you use a play yard as a mobile activity center, toys and sound effects can be helpful.