I buy the brown paper roll used to mask off areas when painting and make crinkle tubes out of it. Brown paper lunch bags are fun too. Toilet paper rolls can be used to make foraging toys. I also tear chunks of paper from the roll I mentioned befor and crumple them into balls and put them in a basket for a dig box. I can post photo after work if you want!
An usused toilet roll. Don't even start to unroll it for them. Just put it in the cage. Eventually, when they have figured out its a roll of bedding, they will rip it up, chew it up, and they will drag it around the cage. Its so fun to watch!
You can make a lot of chews and little toys for them to stash out of all kinds of things. Wine corks, fleece remnants, alphabet blocks from petco are cheap and already have holes in them, large beads (got those from good will), sisal rope, raffia you can get from the dollar tree. Stuffing raffia through a hole in a piece of wood or wine cork till it's really firm and then just pull it so it makes a little fan on each side, everyone likes that to chew and hide. If you want it more colorful you can use food dyes on the woods, sisal and raffia.
Bird perches are fun to put all kinds of things on too. You can wrap it partially with rope to make a good climbing place. Then on places with no rope you can put a roll of party streamer or toilet paper for them to unwrap.
Coconut shells can be made into swings or a place to put food-hang them with some rope.
Mine will do almost anything to get to millet spray-so I tie that up in several places with sisal rope and hang it in hard to reach places in the cage. They have to hang, climb, dangle to get a piece-good exercise and a healthy treat. You can weave it through several baby rings as well and hang that.
grow a small patch of wheat grass. They love to chew, eat and dig it up.
Give them packing paper or other safe paper (like napkins)-don't tear it up-let them do it to make a nest.
Here is the same paper used for a crinkle tunnel. I use the spool for ribbon or tape and glue the paper to it with school glue since it's non-toxic. You can leave it open like this or glue both ends to spools. When it is chewed or soiled I remove the paper from the spool and make another until the spool is ruined!
Also since my ratties are big chewers I make hammock out of felt squares. They cost 25 cents and I just poke holes near the corners and zip tie the to the to of the cage or under the shelves. I also have a tissue box house in this one!