Cardboard Boxes Homemade RattyRat's Review: Rats love boxes. You can leave them as is, or cut holes into them. They can be set out separately, or stacked into one another creating nooks and crannies to explore. What's even better is if you fill the boxes with stuff for your rats to crawl through, such as shredded or crumpled paper, corn starch packing peanuts, cloth, bags, toys, anything that is rat safe to chew on, and climb through. As they become soiled, simply throw them away, and find new ones. Very small boxes can be used as fun interactive toys. Put a couple treats in a small box and seal it up. Then give it to your rats to open up like a present.