Put several natural whisk brooms in the cage. They are inexpensive and provide a texture that birds find appealing. Natural perches with bark offer an amusing distraction. Tie leather and sisal strips to the cage bars. Making sure pieces are short enough not to cause a safety hazard.
Birds can become entangled in long pieces of leather or sisal.
I personally do not allow any rope toys or rope pieces in any of my bird cages. They pose too much of a risk of fraying and entangling a bird. Rope toys should only be given under direct supervision. Fraying pieces of a plastic milk jug are another inexpensive toy distraction. Attaching wireless clothespins to cage bars is another great way to stuff the cage.