I get a little out of control when I go shopping, especially when I go shopping for food. Everything looks good to me! Oh, my favorite brand of chips are on sale; put that in the cart. I really need to eat better, so let's toss in a few veggies. Can't forget juice with my shiny new coupon! But as I try to save money by picking only items that are discounted, I realize I still spent way more than my weekly budget. I look at my cart and think, "Nothing in here was THAT expensive, so what gives?" Well, what gives is many little things can add up quickly, and if you pay attention to what you're buying, you'll realize some of those little things were kind of a waste.
The solution I've found for this is having a calculator on hand when I go shopping for anything more than a few particular items. I pull out my phone, punch in the price for my chips, veggies, and juice and find out that Oh, that juice actually put me over my budget. Best put it back and not keep adding to the cart. If you're the type of person that really likes to plan ahead, it might help you to make a specific list based on your budget and stick to it, but taking a calculator to the mall or the like may still be pretty helpful.
For extra saving-suggestion-goodness, consider the cost of the items and what they add to a meal: Potato chips, on sale, are usually about 2 dollars (for me, anyway). A bag of potatoes is about 3 dollars. If you swapped out a handful of chips for half baked, boiled, or mashed potato, you would end up saving money because the bag of potatoes is more cost efficient per serving. Let's generously assume there are 10 servings in a bag of chips (which is the serving size, but no one ever reminds me by the time I'm done munching down!) for 2 dollars. Let us also generously assume there are 10~ medium to large sized potatoes in a 3 dollar bag of potatoes. Chips are about 20 cents per serving while potatoes are about 15 cents. Add into consideration that chips are consumed more quickly (due to convenience and deliciousness) and that it's harder to snack on a vegetable that usually needs about 45 minutes to cook, you'll find that the bag of potatoes will really help you save. Another example is the ever-popular bag of ramen noodles: There are 6-8 servings per 1 dollar package, which is a great deal. Look at the items in your cart and determine how much the meal would cost using these ingredients. I try to keep meals under two dollars and if you can find items that give you multiple, satisfying meals for a single dollar, then maybe it should replace some of your more popular picks.