Some people like to treat this as a lazy Sunday. While it's great to take extra rest and prepare your body for the work that will come tomorrow, Sundays are also a great time to prepare your meals ahead of time for the week.
Cook your lean proteins, complex carbs (like potatoes and rice), and vegetables in batches so you can easily apportion them whenever you need to. Planning ahead will also help you avoid restaurants or running into a gas station for an unhealthy snack when you're hungry. Preparing your food in advance lets you to throw together quick meals when you get home after a long day at work or from the gym.
Get your beauty sleep, because tomorrow calls for another week of hard work!