Bird kabobs, seagrass mats, vine balls, and shredded paper (inside toys) are my bird's favorites. Other than that, cardboard, finger traps, vine chains/stars/other shapes, sola wood, and palm flowers are also great toys.

There's also packs of toys like this finger trap one and this, but they have potentially unsafe hangers. In my experience, I would stay away from harder woods like pine and balsa because cockatiels have weaker beaks, so they're more drawn to softer, more shreddable objects.