An Easter egg in the Captain Marvel trailer confirms that the movie will involve The Avengers' Project P.E.G.A.S.U.S. - a subtle tie to the Infinity Stones. Captain Marvel seems to serve as a prequel to the entire Avengers franchise, revealing a never-before-seen early adventure of Nick Fury and Phil Coulson. It appears to show just why Fury became a believer in superheroes, with Captain Marvel serving as the inspiration for the entire Avengers Initiative. But it looks as though the connections may run a lot deeper than that.
Project P.E.G.A.S.U.S. is lifted straight from the comics, where it was envisioned as a scientific base in the Adirondack Mountains. It was originally intended to oversee research on alternative forms of energy, but it gradually became a center for some of the world's most advanced technology. The MCU version was first referenced in Iron Man 2, which revealed that Howard Stark had been involved in the project prior to his death in 1991. It was finally seen on the big screen in The Avengers in 2012, when Loki infiltrated its facility in the Mojave Desert.
The second Captain Marvel trailer has finally confirmed that Project P.E.G.A.S.U.S. will appear in the film. One scene in the trailer sees Nick Fury and Carol Danvers steal a Quinjet - one with a P.E.G.A.S.U.S. logo on its wing. It looks like Fury has taken Captain Marvel to a P.E.G.A.S.U.S. base, which makes sense; the Captain Marvel teaser showed a Quinjet flying into space, and even modern Quinjets don't have that capability. But a P.E.G.A.S.U.S. Quinjet - probably a rarer design, built as a result of a partnership between S.H.I.E.L.D. and NASA - could well be able to do that.
The P.E.G.A.S.U.S. reference is important for another reason, however. It's important to remember that, in The Avengers, the P.E.G.A.S.U.S. base in the Mojave Desert was the place where S.H.I.E.L.D. was researching the power of the Tesseract. Given the Mojave Desert is primarily located in southern California and Captain Marvel takes place in Los Angeles (while on Earth), it's quite likely this is the same facility. The Space Stone was retrieved by Howard Stark sometime before his death; he used to work with P.E.G.A.S.U.S., so it's possible he studied the Tesseract there, and that it remained at the Mojave Desert installation until Loki's arrival in The Avengers movie.
It's interesting to note that Ben Mendelsohn's Captain Marvel character Talos, the Skrull war-leader who has used his shapeshifting powers to infiltrate S.H.I.E.L.D., appears to lead a security team at the P.E.G.A.S.U.S. base. Is this just a coincidence - or have the Skrulls targeted this specific installation for a reason? The Tesseract may actually be an important part of Captain Marvel's plot; perhaps the Skrulls have learned that the Space Stone is on Earth, and their entire invasion is really an attempt to acquire it. There's a comic book precedent for that idea; in 2007's Secret Invasion event, the Skrulls focused a phenomenal amount of effort on capturing the advanced technology kept at P.E.G.A.S.U.S., and they could have the same motive here. If this is indeed the case, and if the Tesseract does play a part in this film, then Captain Marvel won't just be a prequel story for the Avengers franchise; it will instead set the scene for the entire MCU.