Toys and chews are absolutely essential for the well-being of your rats. A bored rat may quickly become territorial or destructive - and given that they have the intelligence of a 2 1/2 year old human child, keeping their minds occupied can be challenging. 

Rat teeth never stop growing and must be worn down through chewing and biting, or else the teeth will overgrow and the rat will starve. Always leave a variety of chews of different shapes and hardnesses in the cage. A chew may be ignored for weeks, then bitten to shreds, depending on the rats' needs at any given time.  

Anything that goes into a rat cage will be jumped on, chewed on, and peed on, so items should be non-toxic, and either washable or replaceable. With those guidelines in mind, the sky is the limit! Rats love boxes, old paper towel rolls, used paper cups, sections of dowel rod, round wooden balls (a favorite amongst my colony members) - and that's without getting into the plethora of commercially made toys.

Rats need places to sleep and hide, so be sure to include hammocks, swatches of old fabric made from material that won't fray into potentially dangerous strings, old hats, plastic igloos (another personal favorite of my critters), overturned boxes, and the like for them to "hide" in, under, and around.