Willow and fruit branches or manzanita which can be bought at most pet stores, or dowels of various size and shapes. Three-fourths of an inch is a good starting size. Toys Important for mental stimulation. Change them often to keep your bird from getting bored. Have a few different ones and swap them occasionally.
Ladders are fun and provide exercise for the feet and legs.
Rings, swings and small chew toys are nice. Check each toy to be sure that it is a bird safe toy. Grit Cockatiels do not need grit. They crack their seeds and just eat the inside. They love cuttlebone and it is a good source of calcium.