If your cavy can do this, it will invariably end up peeing or pooping in the supper dish, effectively soiling all the food therein. In addition to the food bowl, you may want to purchase a hay rack, especially if you use hay as your bedding. The rack will prevent the hay from becoming soiled by urine and droppings, keeping your guinea pig's daily supply fresh. The hay rack mounts on the outside of the cage, and the guinea pig pulls the hay into the cage to nibble. Some guinea pigs like to play with their hay racks, too, tugging on long strands of hay and pulling them out for fun.
Some people like to mount a salt or mineral wheel in the cage.
Although it's not necessary for a guinea pig, some pigs do like them, and they last practically forever. For terrain and variety, many people like to add rocks, bricks and tubes to their cage. These not only provide rough surfaces for wearing down claws, but also hiding places and things to climb on or around to help alleviate boredom. Bricks are especially cheap and rocks are often times free. The PVC plastic is hard, durable and easy to clean.