What Can I Use As A Substitute?

I too have bad eating habits, not a lot of veggies, some fruit, LOTS of bread and potatoes, the only thing I can do to keep from eating the junk food is to not buy it, don't bring it in the house... Then stock up on the fresh fruits and veggies you will eat... Clean them and set them out... If I set out a relish or fruit tray, it is gone in no time, because everyone, including myself, grabs from it when they walk by it. Then try to eat your main meals on a regular schedule to fight off hunger and cravings....when I go without the junk food for awhile, I find I don't want it as much... But when I really have to have something, I shoot for the crackers and cheese, or 100 calorie packs. You didn't mention what find of veggies you like but from one picky eater to another, shout at me and I'll try to help with recipe ideas....

If you like fruit, eat it. You can also use dried fruits (natural, not the sweetened kind). I use dried mangos, apples, apricots, cherries and cranberries to help with my hunger cravings. You could also buy fruit leather (a natural fruit roll-up) at health food stores. You can also freeze bite-sized fruit to munch on (grapes, cherries, berries and pineapple chunks are some of my favourites). Frozen fruit is also great for making smoothies. In summer I also blend fruit to make popsicles.
I'm also not a huge fan of vegetables, but I find that the sweet crunchy ones tend to be my first choice (carrots, sweet bell peppers). Because I don't like vegetables, I tend to hide them in my meals and use fruits to snack on. That way my family also benefits from the vegetables. It is easy to blend up some extra vegetables into a tomato sauce or a soup.  Hope these hints are helpful to you.

Eat more of what veggies you do like.  I love eating a raw cold bell pepper, or cucumber.  Substitute the bad for the good things you do like.  If your craving something sweet, eat watermelon or some melon.  Hope this helps.  Good Luck.