Plan, plan, plan. I make batches of healthy snacks which need no refrigeration. Example : sugar free meringues, I change the flavouring often so I don't get bored ; meat crisps (put lean meat in the oven until it is crispy). I keep tupperwares at work and home, and refresh them regularly. That way if I have a pang for something sweet or salty I do not have excuses to make poor choices.
If you are not creative, look on the internet or Spark Recipes. Loads of people invest time in sharing their diet culinary successes so you can enjoy them!