What else should I put in my guinea pigs cage!?

Her cage is the Designer 40 inch Small Animal Habitat from Petco. It's 40 by 21, and has a ledge on it(took off ramp cause she just jumps up!) so far on the ledge I have her treat kabob, her food and water bottle, and on the main level I have a pile of hay, and a medium igloo! And thing else she needs? Toys or other wise! Thanks!:)