Target is offering 15 percent off everything online today — here's why you should stock up

For today only, Target is offering 15 percent off its entire website.

That means you may want to stock up on things you're going to have to buy anyway, like toothpaste or shampoo.

As Mark Cuban says, it's smart to buy in bulk and on sale: "It's so hard to make a return on regular investments that … you're better off buying two years' worth of toothpaste when it's on 50 percent discount. There's an immediate return on your money."

This strategy applies to "any reusables or consumables that you have to have," the billionaire told Vanity Fair. "When they're on a huge sale on Amazon, buy them, because chances are, their prices are going to go up. That's a real savings that you get to put in your pocket."

Target's 15 percent deal comes in addition to its other Cyber Monday deals, which include 30 percent off kids' clothes and shoes, women's and men's sweaters, fleeces and boots.

Plus, you can probably score generous deals on electronics, holiday decor and toys and gaming, Dealnews reports. The retailer is offering a 50-inch Samsung 4K TV for $479.99, for instance, which is 44 percent off the regular price, and $20 Target gift cards if you buy BeatsX earphones or Beats EP headphones.

But don't buy anything simply because it seems like a "good deal," warns "Shark Tank" investor Kevin O'Leary: "If you're spending money on something you wouldn't have bought otherwise just because it has a '50 [percent] off' sticker on it, you're still throwing away your hard-earned dollars."

Instead, make a list and a reasonable budget, and stick to them both, he tells CNBC Make It: "If you have a shopping list of items that you know you'll be purchasing over the next few months regardless of price, waiting for [holiday] sales is the most financially responsible option."

Disclosure: These items have been handpicked by our editorial team. CNBC has affiliate relationships with some retailers so, in some cases, if you purchase an item listed here, we may get a small share of the revenue from your purchase. This holiday season, the proceeds will be donated to the Council for Economic Education, which supports economic and financial education.

Like this story? Like CNBC Make It on Facebook!

Don't miss: Mark Cuban: Why you should buy a two-year supply of toothpaste