The best diet for a ferret is one that consists mainly of high-quality commercial ferret food that is formulated to meet their specific nutritional needs. Additionally, you can supplement their diet with small amounts of fresh meat, such as chicken or turkey, and occasional fruits and vegetables as treats. It is important to avoid feeding them foods high in carbohydrates, sugars, or dairy products, as these can lead to health issues for ferrets. Always make sure your ferret has access to fresh water at all times.