It's really important to put some effort into enriching your pets lives, and this is no exception with pet rats. Keep in mind that rats tend to be animals that are going to spend the majority of time in their cage, and it's important to have various forms of enrichment for them so that they have things to do and things to entertain them.
Most commonly people will provide them with nesting type materials. They like to shred, they like to chew. Sometimes it's as simple as a handful of paper towels that they can tear apart and build a nice big nest to hide in. Some things to put in the cage that often are good for them, maybe blocks to chew on. They may like to have stuffed animals to carry around or to play with. Other things for rats to use sometimes are the hanging types of bird toys that people sometimes think of for large birds. They're rope, they're pieces of leather, they're wooden blocks, they're safe, they don't have any artificial chemicals on them. And it provides the rats, if they choose, with something to chew on, something to play with, ropes to shred.
Another thing that rats like that maybe is not a toy are hanging hammocks and hanging beds in their enclosures. They will very often spend a lot of time shredding them, chewing them. They often decide that they want to create a bed, and they create a very fluffy burrow type bed, so they'll not consider it a toy. Providing them with safe materials to chew up. Providing them with things to shred. Providing them with pet store cotton that's safe to use with small rodents for them to shred and create a nest as well.
In most cases, they're not necessarily going to play with toys, but it's good to provide them with forms of enrichment such as things hanging in the cage, things they have to climb to reach, you may want to put certain treats in certain areas that provide them with the means to have to get to that treat so it's not as readily available so it in a sense gives them things to do. But wooden blocks to chew on, they may prefer to have other types of small child's toys like plastic rings, and some rats will actually use these, carry them around and play with them .
So just keep in mind anything that seems safe, anything that seems like it's not something they could chew and ingest and potentially lead to health problems, but anything that's going to lead to a more enriching cage lifestyle is going to be an appropriate toy. Not to mention the old fashioned toilet paper cardboard rolls or paper towel cardboard rolls. Rats will sometimes climb through these, use them as tunnels, and they'll actually chew them as well and use them as bedding material.