This is a real challenge in my household, too. With our office in downtown Houston, there are so many places to eat, and because I'm usually running around before I go into the office (when I go... my office is usually the house!), I don't take lunches with me because they'll spoil in the heat. And my husband doesn't do the whole lunch-taking thing.
Plus, we have two boys, one of which is a good eater, and the other who is a challenge to feed because of his limited number of "likes". If he could subsist on chips, he would.
Even though I have never really bought a lot of junk food at the store, I am making even more of an effort not to do so. I want my family to think of junk food as "treats" and not as "food groups" or "meal accompaniments".
I make it a point to pop fresh (not microwave) popcorn usually once a day. The kids love to watch, and everybody loves to eat it. With just a little sprinkle of salt, it's better for everybody than chips. I've begun serving popcorn with sandwiches at lunch so everybody can satisfy their "crunchy food" need.
I make my own popcorn chicken instead of buying prefab nuggets. Cut up boneless strips, dredge them in a little flour/salt/garlic powder/pepper, and fry them in just enough oil to turn them around and not stick to the pan. The kids love it.
I buy yogurt for the kids and me and make pudding for treats. Every bit of extra calcium helps. I also make popsicles out of fruit juice so the kids get their frozen treat fix without getting more "bad" sugar.
I insist that everyone- even Mom- eats a fruit or a vegetable at lunch and dinner. I buy a few kinds of fresh fruit- everyone in the house eats apples and grapes- and quick-fix veggies to serve with Ranch dip. Cucumbers, broccoli, sugar snap peas, mini carrots. The kids are still shying away from the veggies for the most part, but if I keep buying them and putting them on their plates, eventually they'll eat them. My older son will eat just about any kind of cooked vegetable- he just seems to have trouble with raw ones. I also schedule nights to make salads with dinner, and I mix up the ingredients as much as I can so my hubby doesn't get bored.
For a treat, sometimes I will buy chocolate-flavored soy milk. I first did this at my older son's request- he pointed to a carton and asked for it. I was sure he'd be disgusted when he found out it wasn't cow's milk, but nope, he liked it, and so did the little one.
When I make pancakes for breakfast, I throw in some chopped fruit- usually blueberries or strawberries.
I looooove cheese enchiladas, but I can't chow down on them anymore. When we eat Mexican food out, I order a combo plate with a taco or tostada and an enchilada. I get a little less fat, and I appreciate the enchilada more.
We are still learning how to eat more healthfully, but with us in transition like you, I thought it might help to know what some of your first steps could be.

Good luck!