You have to break the cycle. Find one hour, on the weekend or a day off, wake up earlier or go to bed later if you have to, to plan and prepare meals. Go to the grocery store and get healthy food items and snacks (see this post for recipe ideas), ziploc bags and containers. Start portioning out meals - for instance, make 3 sandwiches, fill 3 bags with a handful of nuts or cereal, and put 3 apples or granola bars in a bag. Put them in the fridge and for the next 3 days, you can grab it and go before school or work. Prepare and repeat for as many days as you need to. With some planning and thoughtfulness, you can definitely make time to eat well - practice making easy, healthy meals that store well whenever you find spare time and eating becomes a lot easier.