When you are dealing with a person and you accidentally drop an item such as your cuff keys, ticket book, subjects I.D. card etc, do not immediately bend down to pick it up while in close proximity to the subject.
When possible, utilize a cover officer. You can also direct the subject to walk several steps away and turn away from you. Then, while keeping the dropped item between you and the subject and maintaining visual of him, you can retrieve the item and avoid being sucker punched or kicked.
If the subject is in a vehicle, direct him from the vehicle and secure him in your police car or direct him to another officer that can keep him occupied while you retrieve your item safely.