I try to plan a menu for the week. If I get too ambitions and realize that I have planned 5 expensive meals, I stop and replan. This works better for me than going the the store and winging it. I also print out recipes I find online and tear out the ones in magazines. I take the whole batch with me including a back-up or two so that I can change my plan if the store is out of somthing or the fish or produce I planned to buy looks bad. I second the idea of using what you've got - usually you can stretch the pantry out another day.
I buy most veggies frozen or canned except for a meal or two, because so often I plan something and wait to long to make it, and the veggies are rotting in the drawer.