Two Things

1. Keep a "Do We Need?" list. Before either of us even consider a trip to the store, we look at the "Do We Need?" list (usually while wandering around the house), which includes things like milk, cat litter, laundry detergent, toilet paper, etc. Because nothing breaks our budget more than lots of trips to the store because we didn't realize we were almost out of something that we really need. And yes, pop is something we really need. ;)

2. Know how long things last. My kids go through a gallon of whole milk about every four days. We keep track of toilet paper and cat food and other things like that so that we know exactly how much we'll need in a given pay period. Sounds hard, but if you only go to the store every other week or so it gets easier. Or, you could just write the date you started using the item on it in permanent marker.