I don’t have any of these ‘must haves’ especially for my chickens and didn’t need them either. Maintaining a healthy flock is to provide good shelter, good food and a large area to search for food. But if you have a large flock or live far away from stores it probably is a good aid kit to have.
The only ‘medicines’ I have ever used are mainly to prevent issues. Such as garlic, apple cider vinager, diatomaceous earth, tabacco and lavender. Mainly to prevent worm and red mite infestations. A few times I had sick chickens, but good care and time where enough to heal them. With chicks I took some losses. But most of them healed too after time.
If a chicken gets injured I will use my own bandage and means to heal her. If my flock gets in some kind of trouble I will go to the store to buy what I need.