Plan your menu so that you have leftovers to eat later. For example:
Sunday: Pot roast and vegetables (potatoes, carrots, etc)
Monday: Salad with Tuna or chicken, bread
Tuesday: Spaghetti (make your own sauce and freeze the leftovers for use later), salad, garlic bread
Wednesday: Baked chicken, mashed potatoes, carrots
Thursday: Leftover pot roast sandwiches, chips, salad
Friday: Pizza, veggie sticks
Saturday: Lasagna, salad, garlic bread
Sunday: Stew or soup, rolls
Buy in bulk when you can, but not produce unless you can eat it quickly. Check the papers for grocery store specials and stock up then. Your freezer is your friend - portion leftovers and freeze for later use. Frozen vegetables are just as good as fresh, last longer and are often on special at the grocery store. Look for farmer's markets in your town - local is fresher, lasts longer and might be less expensive.
Lunch can be leftovers from the night before, a package of ramen with a little chicken and frozen vegetables added, soup, etc. If you like sandwiches, try what my Dad used to do: make up a week's worth of sandwiches (lunch meat, cold cuts, balogna, peanut butter & jelly) and freeze them. Take one out in the morning and by the time lunch rolls around it'll be defrosted and ready to eat.