It’s typically one of the biggest sales of the year. And in 2021, Amazon Prime Day could be even bigger.

The annual two-day shopping event is set to kick off at 3 a.m. ET on June 21 and will include discounts on more than 2 million items for Prime members — about twice as many as last year.

EMarketer is forecasting that total digital sales in the U.S. on Prime Day will jump 17.3% year over year to $12.18 billion. Sales made exclusively on Amazon on Prime Day will grow 18.3% from 2020 levels, to $7.31 billion, it said.

“That is an incredible number,” said Dave Kender, the editor in chief of Reviewed, but “most of the products are not that interesting.”

“There are diamonds in the rough,” he added. “You just have to work to find them.”

More from Personal Finance:
Suze Orman’s best advice for small business owners
Early signs that you have a spending problem
Here are some money moves while the Fed keeps rates low

Naturally, Amazon-branded products will be heavily discounted, including two-for-one sales on the Echo Dot and Fire TVs starting at $99.99.

Other stand out sales include Apple AirPods with a charging case marked down 25% to $119.99 and a Shark IQ Robot Vacuum for $319.99 — a savings of $280.

It’s a great time to start stocking up on summer travel supplies or back to school gear, especially from small businesses. Brooklyn-born bag company State will offer half off a kids backpack, which normally retails for$95 and Rockland has a rolling duffle bag for $50, about 55% less than retail.

This year some of the very best deals will be on small kitchen appliances like electric kettles and coffee makers, according to Nathan Burrow, the senior deals editor at Wirecutter.

Burrow predicted air fryers could be one of the most popular items overall, outshining even the Instant Pot, which has remained one of the hottest sellers for years.

Of course, you must be an Amazon Prime member to take advantage of Prime Day deals. 

If you haven’t already joined, it’s free for 30 days. After that, you can cancel or sign up for a month-to-month membership for about $13 or pay $119 for the year. For deal hunters, note that membership also includes free music, movies and e-books, as well as discounts on groceries at Whole Foods.

Then, download the Amazon app, scroll through upcoming deals and mark the items you are interested in as “watching,” Ramhold advised. You’ll receive a notification when the price drops.

When a deal is live, add the item to your cart immediately. Some offers sell out quickly, Ramhold said. Once it is in your cart, you’ll have 15 minutes to decide whether to complete the purchase.

If there is a specific product that you are set on and you don’t see it in upcoming sales, you can create a wish list and Amazon will alert you if it does become part of a Prime Day deal.

However, some of the best bargains are not exclusive to Amazon at all.

Walmart, Target and Best Buy are holding competing deals events — as they have in previous years — to coincide with Amazon Prime Day 2021.

Already, Best Buy is selling the Roku Express for just $29.99 and Jabra earbuds for $179.99, a $50 discount. During Office Depot’s discount days, which run from June 21 to June 23, an Acer Chromebook will be marked down 25% to $169.99.

But buyer beware. As vaccination rates increase and the economy bounces back from Covid, post-pandemic sprees — or so-called revenge shopping — can quickly lead to overspending, according to a recent report by the American Institute of CPAs.

Already, 2 in 5 Americans said shopping online more has made it harder to stick to a monthly budget.

About 39% of those polled said they often don’t know how much they’ve spent on their credit or debit card until they see their monthly statement.

“Merchants have powerful strategies to encourage you to spend,” said Neal Stern, a member of the association’s financial literacy commission.

“Determine what you plan to purchase and how much you’ll spend before you start shopping,” he said. “If you have a plan, you’ll be less likely to give into overspending.”

Also, before checking out, always look to see if there are better deals elsewhere, Kender advised. Open a new tab and search the product’s model number to see prices from other websites.

And finally, read user reviews and research price histories so you can determine how good the product — and discount — really is.

“There is no such thing as a good deal on a bad product,” Kender said.

Subscribe to CNBC on YouTube.