Simply stick a shopping basket under your shopping cart. Place the items from your grocery list into your cart, and place any “extras” that entice you in the basket below.
It may sound strange to wander through the grocery store with both a cart and a basket, but it's all part of a system that can save you some serious change.
Now, you can easily calculate the total cost of your essentials when they're the first thing you see, and those other items will more likely be “out of sight, out of mind.”
Once your cart items are scanned, you'll know how much is left in your budget, and you'll easily be able to figure out how much you can spend on those “shopping basket” items.