It so hard not to slip up when your unorganised, but most shop have a healthy alternative. There is a Topaz near to my work where, previously, I would have bought all things unhealthy.
But they do an amazing selection of salads and healthy snack pots. They also display the calorie content on everything, which help make better choices. They have a massive selection of salad dishes and are reasonably priced. These are my go to lunch when in a rush for work or unorganised with food.