• Retail traders sent almost $30 billion into Nvidia shares in 2024 on balance, according to Vanda Research.
• Artificial intelligence was the story of the tech market in 2024 and was the catalyst behind some of the biggest individual gains.
• December's peak shopping days are closely followed by the busiest month for sending items back, which experts dub "Returnuary."

Here are five key things investors need to know to start the trading day:

1. The morning after

Stock futures were lower Thursday as traders came back after markets were closed on Christmas Day. Futures tied to the Dow Jones Industrial Average fell 150 points. Meanwhile, S&P 500 futures slid 0.3% and Nasdaq 100 futures dropped 0.3%. Follow live market updates.

2. A gold mine

Retail traders sent almost $30 billion into Nvidia shares in 2024 on balance, according to Vanda Research. Vanda data showed that Nvidia's net inflows have seen a nearly nine-fold jump from 2021. Inflows tended to spike this year around Nvidia's earnings reports, and retail investors also bought in during an early August dip in the midst of a broader market sell-off, according to Vanda's Senior Vice President Marco Iachini. The chipmaker is on track to be the most-traded stock this year, dethroning Tesla, the retail investor favorite that earned the most-bought title in 2023.

3. Tech's big winners

Artificial intelligence was the story of the tech market in 2024 and was the catalyst behind some of the biggest individual gains. AppLovin had the biggest individual percentage gain, growing more than 700% from a market cap of about $13 billion to more than $110 billion, as the company centered its business around online ads and booming profits from advancements in AI. Crypto was the other big driver, particularly after President-elect Donald Trump's victory in November. Shares of MicroStrategy jumped 467% this year from a bitcoin-buying strategy that's made founder Michael Saylor a crypto cult hero, as the company has purchased over 444,000 bitcoins since 2020.

4. 'Returnuary' is almost here

December's peak shopping days are closely followed by the busiest month for sending items back, which experts dub "Returnuary." Returns are expected to rise to 17% of all merchandise sales in 2024, reaching $890 billion worth of returned goods, according to the National Retail Federation. That's up from about 15% of total U.S. retail sales, or $743 billion in returned goods, in 2023. But the growing amount of returned merchandise is a major problem for retailers and comes at a high environmental cost.

5. The Juan Soto effect

Skyrocketing salaries and deals for top athletes and college players have initiated a new gold rush among wealth management firms. Juan Soto's $765 million contract with the MLB's New York Mets highlights the massive wealth that's being created by pro athletes, and wealth managers are expanding their sports segments and hiring former athletes to recruit more clients. Unlike most wealth creators, who create their wealth as they get older, athletes make their biggest windfalls at a young age. This can create more opportunities for managers, but can also provide unique risks when dealing with a 20-something year old or, increasingly, even a teenager.

— CNBC's Yun Li, Alex Harring, Ari Levy, Jessica Dickler and Robert Frank contributed to this report.