Clutter is an evil we all have to fight, and if you've ever discovered that you bought something you didn't need -- spaghetti sauce, for example, when a jar was hiding in the back of your pantry -- doing an inventory and making "do not need" lists may help.
Aloysa on My Broken Coin suggests a couple of places where these lists can be put to use: In the bathroom, you might fight scores of cleaning supplies, shampoos and shower gels. The pantry and freezer are two other obvious spots to check; a "do not need list" will keep your actual shopping list shorter.
Also take a look at your closet and do an inventory before you go clothes shopping. (I'll admit to spur-of-the-moment clothes purchases for my daughter where I would've saved some money if I had this "do not need" list.)
How "Do Not Need" Lists Can Save You a Buck [My Broken Coin]