Hit the Dollar Store....
Plastic army men/dinosaurs/bugs
Plastic ping pong/golf balls
Barrel of Monkeys
FREE: milk/water caps. Snip the rings off the bottles and toss them in as well. Make sure you snip tho so they can't get them stuck around their necks.
Strips of fleece are good also.
This yellow/green plastic ball I got at WalMart in the Spring in their seasonal section. They work well because I can put mealies in the bottom and set it in the pit. The mealies can't crawl out and as you can see, the gliders love digging inside for the treat.