For most of us Sunday is a day of rest, a reset for the week ahead.
A well deserved rest day is always welcome, but Sunday's should also be used to make sure we are ready to face the week with our best possible plan to be healthy and stay healthy. So some good things to do on Sunday is plan your meals for the week. Meal planning has been my weak spot in this healthy living journey, but I know that the weeks that I took time to plan out my meals for the week were indeed my best weight-loss/fitness weeks. I believe at the very minimum, you should plan out your breakfasts for each day as it sets the tone for the day, and gets your metabolism going.
I love anything that is "grab and go" easy, most mornings I have a fruit smoothie to start my day, but for the days I go to the gym in the morning I definitely need a little more than that, so having something easy is great. Some things you can prepare ahead on Sunday are hard-boiled eggs, egg muffins, and overnight oatmeal (follow links to my Pintrest). I also do some plan ahead dinners like meatloaf muffins, and some crock-pot recipes.
In addition to meal planning, be sure that you are ready for your workouts for the week. Get your workout clothes ready, and make sure any gear you may need is easily available. The WODs for my gym are posted the night before, so I don't always know what I will need each day until the day of, but to make sure I have everything I may need I keep gloves, my jump rope and a few other things in my car. I also put my workouts on my calendar with reminders, this helps to keep me accountable; whenever that reminder comes up I am either happy because I am ready to go, or feeling guilty if it looks like I may miss out on a workout.
Even if you can't plan your time, meals, workouts down to the second, be sure to plan ahead to incorporate everything, this way you will do your best to get it all in.