WATCH: The best and worst foods to buy in bulk

Many people opt to buy grocery staples in bulk because it can be an economical way to fill your cupboards.

Often, items are less expensive per unit and you get to control exactly how much you buy. However, there are some exceptions to the rule.

Items you should avoid at the bulk store:

• Flax seeds: The oils in flax can become rancid very quickly if they’re not stored properly. Since they are exposed to heat and light in the bulk bins, they won’t be as fresh as if you bought them packaged. Once you’ve purchased them, keep them in your freezer in an airtight, opaque container to extend the shelf life.
• Flour: Unless you’re baking several cakes a week, it’s better to buy flour in small, packaged amounts because of its tendency to go bad fairly quickly. Like flax, it’s best to store flour in a cool, dry place in an airtight container.
• Nuts and seeds: Although many items are cheaper to buy in bulk, nuts and seeds tend to be more expensive per unit in bulk.

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READ MORE: 5 things you should buy in bulk

Best items to buy in bulk:

• Dry pastas, grains and beans: Not only are these items always good to have on hand to whip up a quick meal, but they store well and have a long shelf life.
• Sugar: The sweet stuff can be quite pricey in packaged form, but its long shelf life makes it the perfect bulk purchase. Throw in an apple slice in an air tight container with your sugar to keep it from hardening.
• Spices: Dried herbs and spices often come packaged with much more than you need. Buying spices in bulk lets you control the amount you get to ensure freshness every time you season your dish.