I work lots of hours and starting to feel unfit and putting on weight due to lack of exercise and junk food on the go. how can i change this?

Wake up earlier: I would try waking up earlier, jog2-3 miles or ride an exercise bike for 30 minutes before work and begin eating healthy foods( salads) instead of junk food. Best of luck!

Eat real food: You already realize that you're eating junk food so make changes there. Fresh vegetables and fruits, fresh meats, healthy fats (avocados/olive oil/butter/coconut oil), limited sugars and starches. Quality sleep is also very important - at around 7 hours per night. Then do some kind of exercise that you enjoy 2-3 days per week.