Warehouse clubs like Sams Club, Costco and their ilk are some of the most popular places to shop in the United States today. Because they allow a customer to make bulk purchases, the cost of the items being purchased can be reduced significantly. One problem however is that shopping at a warehouse club can actually perpetuate a number of negative shopping habits like over buying that, in the end, will have a negative effect on the person’s financial health.

To that end, if you’re diligently trying to stick to your monthly grocery budget, the mistakes that we’ve listed below should definitely be avoided when you head out to your local warehouse club with your weekly grocery list. Enjoy.

Mistake: Buying large amounts of perishable food. Here’s the thing; unless you are 100% sure that your family will be able to eat that case of strawberries or finish that 5 pound package of guacamole before it goes bad, you’re definitely going to be wasting money on food that’s eventually going to end up in the garbage. Simply put, if you have to throw half of your purchase into the dumpster, it doesn’t matter how cheap it was or how much of a discount you got when you purchased it. Better to plan your meals for the week in advance and, if you are sure that you be able to get rid of that fresh produce before it goes bad, go ahead and purchase it.

Mistake: Depending on your warehouse store for all of your groceries. Even though they have prices that are in most cases better than what you’ll find at your regular grocery store, the fact is that if you use coupons and take advantage of their weekly deals, your local grocery store will sometimes actually have better prices and, since they may be closer to your home, you’ll save money and time going there. Even more, if you can find deals on perishable food in smaller quantities you won’t have to throw a lot of it away because you had to buy too big a quantity for your family to finish.

Mistake: Going shopping without a list. While many people use a list when they go grocery shopping at their regular grocery store, not nearly as many do the same when going to their warehouse club. This tends to lead to much more impulse buying and money spent on things that you don’t really need, can’t use right away or might spoil before you’re actually able to use them. If you’re keen on keeping your budget on track and not overspending, having a list and sticking to it when you go to your warehouse club is a definite must.

Mistake: Ignoring your warehouse club’s website. While the prices inside your favorite warehouse club can be excellent, many times the prices that they have on their website are even better and, since free shipping is oftentimes included, you’ll likely save more when you purchase some items online. In terms of what you should and shouldn’t buy online, nonperishable products and larger items that you may want to have delivered right to your door are a good place to start. Before making any purchase you’d do well to compare prices from other retail stores and online retailers to make sure that their price is truly the best.

Mistake: Ignoring expiration dates on processed foods. Just like it’s a mistake to purchase more perishable produce then you can eat before it goes bad, purchasing packaged food items in bulk that have an expiration date should only be done if the expiration date is definitely going to be longer than the time it takes you to eat the food itself. Before buying any processed foods in bulk, take a good hard look at what they are and how rapidly your family will truly be able to eat them before making your final decision.

Mistake: Forgetting to compare prices. Many people who love their warehouse club make the mistake of forgetting to compare prices because they think that the price they’re getting is already the best. When it comes to high-end and high-cost items like flatscreen TVs, laptop computers, household appliances and the like, taking some time to check prices at other retailers could well save you a significant amount of money. While a warehouse club like Costco might have a great deal on a flatscreen TV, an electronics warehouse store like Best Buy will usually have quite a few more models and may very well have a much better deal on exactly the same TV or something quite similar. Again, a little bit of time doing research and comparing prices may save you 5, 10 and even 20% more.

Warehouse clubs are definitely a great place to shop for all sorts of items and, if you have a large family, may well be the very best placed to get the lowest prices. If you can avoid the mistakes above you’ll not only get great satisfaction out of using your warehouse club membership but also save the most money in the process.