This post is from Angela Colley at partner site Money Talks News.

Bulk stores such as Costco and Sam's Club do have some great deals, but that doesn't mean you'll always save money shopping at one of them. If you're like me, three things are working against you while you push that ginormous cart.

1. You assume everything is a good deal because it's bulk pricing.
2. You really believe you won't let it go to waste.
3. You greatly overestimate your love for one type of food.

Fall prey to those pitfalls and you might end up wasting money. Shop smarter and you'll not only stop wasting money -- you'll start saving a lot of it.

Before we begin, check out this video from Money Talks founder Stacy Johnson about the best deals at warehouse stores. Then meet me on the other side for more.

1. Stick to one membership.

Bulk stores have cheaper prices on most items. A study conducted by the United States Department of Agriculture (.pdf file) showed that 86% of the food items it compared cost less at a bulk store. (The USDA found the largest savings in meat, canned goods and store-brand foods.)

But that means 14% didn't cost less. When you factor in sale prices or store card discounts, it may be cheaper to buy certain foods at the grocery store. To be sure, calculate the unit price for the things you buy at the bulk food store and the unit price for the same items at the grocery store. Then compare the two.

4. Buy the store brand.

Many of the bulk stores carry their own brands of cleaning products, laundry detergent, pet food and some nonperishable foods. And the store brand usually costs less. For example, Sam’s Club sells Tide and their brand, Member's Mark.

• Tide with ActiveLift, 170 ounces/110 loads = $19.98
• Member's Mark Liquid Laundry Detergent, 225 ounces/146 loads = $13.68

In this case, buying the store brand will save you 12 cents a load. Doesn't sound like a lot, but how much laundry do you wash in a year?

5. Split perishables with a friend.

Bulk stores have good deals on fruits and vegetables, but I know I'll never eat 5 pounds of apples, and I don't want to freeze them. Instead, I split bulk packages of perishable food with a friend. We each pay for half, and I get the bulk price without wasting food.

6. Freeze food before it goes bad.

After years of wasting countless perishable items because I just didn't get to them in time, I finally learned to start checking expiration dates and freezing whatever was left before it could go bad.

Check out When Does Food Really Expire for a cheat sheet on freeze times.

7. Don't plan too far ahead.

I have 14 cans of peaches in my pantry. They've been there six months. Why? Because six months ago, I ate a lot of peaches. I thought I'd love them forever.

I didn't.

If you don't have a large household, it can take weeks or even months to use up a bulk size. And if you get sick of it -- or no longer need it -- you've wasted money. You're better off sticking to staples such as flour, sugar or rice and avoiding the giant-sized frozen barbecue shrimp. 

Bulk-food stores come with extras -- a gas station, a tire and car-care center, a cafeteria -- to make the most of your membership. So use all of the perks the store offers. And most extras have a discount (like tires, which are dirt-cheap at Sam's Club), so you’ll save even more.

More on Money Talks News and MSN Money:

• 28 tasty tips to save on food

• Why I never shop at dollar stores

• 10 painless ways to save $1,000

• Big discounts on little pleasures

• 5 ways to trim your grocery bills

• Calculator:Is your budget in balance?