If you have the room in your backyard, you may want to start giving growing a garden a shot. You will have tomatoes and cucumbers in no time at all. The best tip anyone ever told me about going shopping for food when your broke is, never go to the store shopping hungry, and never go without knowing exactly what you are going to get. Make a shopping list and stick to it! I know it is hard to stay away from the sweet stuff, but here is a good rule to follow, if it has a shelf life of over 2 years, or (like a twinkie) doesn't mold as natural bread products would, means its terrible for you. Loaded with preservatives that are made straight in a laboratory. Sure it keeps the companies bottom line high, but who knows what all these food colorings and preservatives are doing to our body in the long term.
I am not sure what your diet consists of now, but I will tell you this, you will need to buy (and eat) more greens. Even if you think you eat your daily value, or whatever the case may be, no one can ever have too much, and its essential for a healthy body, and digestive system. Try to get frozen ingredients or even fresh....stay away from the canned goods. They add too much sodium that just isn't needed, and it definitely isn't good for us. So keep it simple! Well.... Not too simple.
One of the biggest things you can remember when buying your weekly beverage is to try to keep sugar out of the mix. Especially when it comes to soda, and other artificial flavored kids drinks. If you want something refreshing that tastes good, get some fruit juice, you can cheat if you like even and get a 30/40 part fruit juice and artificial flavoring....anything is better than the bucket they pull out of that Coca-Cola syrup.
One of the greatest tricks I ever learned when controlling my bad eating habits was to portion lets say a package of cookies into 10 smaller ziplock bags. This way whenever I wanted a cookie I was forced to grab a ziploc bag instead of the entire case of Oreos. This is a good trick for you and your family if you are trying to eat healthier. Sometimes the problem isn't what we eat its how much of it we eat. Too much of something that good, definitely can't be good for you in the long run.