I'm going to assume you won't change your job or location to create more time in your life to actually do the exercise your body needs.
The next best thing you can do is tune your eating habits. Because you're fighting calories in/out imbalance, and you have no tools to improve the "out" part, you must focus on the "in" part:
* Don't buy calorie-dense foods. Slowly wean yourself completely off cookies, cake, desserts. If they're around, you'll eat them.
* Start shitfing towards a more "vegetarianish" diet. If you eat out, make sure it's a salad, bean salad, tofu dish, stir-fry veggies. Learn to skip the meat and load up on the fiber.
* Replace those 300-calorie Coolatas with a mug of low-fat low-sodium chicken broth. Broth really does kill the hunger pangs and has close to zero calories (30 calories in a 48-oz can).
If you want to avoid buying ever-larger clothes, you're going to have to re-tune your eating habits for the reality you've put yourself into. But you can do it -- it's all about being consious and making choices. Do it one little step at a time, and keep doing it.
"From there to here, from here to there, funny things are everywhere." -- Dr. Seuss