The best diet for a pet turtle typically includes a variety of foods such as commercial turtle pellets, leafy greens (e.g., kale, collard greens), vegetables (e.g., carrots, squash), and occasional treats like fruits (e.g., strawberries, bananas). It's important to research the specific dietary needs of your turtle species as different types of turtles may have slightly different requirements. Additionally, providing calcium and vitamin supplements as needed can help ensure your pet turtle's overall health and well-being.