Eating a healthy breakfast keeps me on track the rest of the day. Because I start off full I don't overeat later.
I also plan a morning & afternoon snack. I fill/take a small personal collapsible cooler with the snacks I can have for the day. I can eat anything inside...guilt free!
Keep ready to eat & fast fix items on hand, like yogurt, mini bagels, cut cheese, lean meats, tortillas, boiled eggs and oatmeal to grab and go when time is a premium.
For snacks, any of the items above work plus veggies/fruit, nuts, whole grain/dense carbs like snack bars, crackers, etc.