Crows are intelligent animals. They need to have something to do to not feel bad. Even when it comes to a short treatment, it would be good if the crow has something to do. As usual, try to adapt everything to the patient’s situation.
If you had nothing to do, no other crows nearby, etc., you could cause permanent mental damage.
So what is a good toy? A plastic cork from a soft drink bottle, a toilet roll, pieces of trees that you find in nature, lego, ….
You should beware of everything that a bird can swallow, everything that is sharp and everything that can be eaten. They do not usually eat paper and cardboard, but they swallow threads and small pieces of plastic (from fabric) and this can cause health problems and death if you are unlucky.