Planning meals for the week keeps me on track with ensure I am providing healthy meals for my family. I buy just the groceries I need for the meals and try to stay away from the extra goodies. In addition, it means evenings are less stressful, and we don't spend as much money ordering in.
My favourite meal planning helpers are the Cooking For the Rushed cookbooks. These have weekly meal plans, as well as grocery lists. The meals are all pretty good, nutritional info is available, and all meals are ready in an hour or less.