You need to get a cooler big enough to take lunch and snacks with you. You can plan out your meals for the week on the weekend. Focus on plenty of protein and fresh fruits and vegetables. Greek yogurt, lunch meat, boiled eggs, veggies and hummus, apple with peanut butter etc. Bring bottled water too. If you get 30 minutes at lunch, eat your lunch then go for a short walk. Once you get the diet under control, you can focus on getting more activity.