There are a few things from Legends that made its way into Episode VII, but there are many more elements that have an uncanny resemblance to things in Legends.
Same as Legends
- Crossguard lightsabers first appeared in Legends, although with a different appearance despite the same name
- "Light" as a term for the Light Side of the Force was first used in Legends
- The word "Starkiller" has existed since George Lucas' original draft of Star Wars and was the code name of Galen Marek in The Force Unleashed
Seemingly inspired by Legends
To my knowledge, there are no statements from anyone working on The Force Awakens that these were intentionally drawn from Legends, but the similarities are uncanny.
- The general plot of the Rebellion successfully restoring the Republic and the Empire living on in different forms and under new leadership is common in Legends material, such as the Thrawn trilogy
- A villain named Kybo Ren existed in Star Wars: Droids: The Adventures of R2-D2 and C-3PO
- Kylo Ren's mask seems suspiciously similar to Darth Revan's mask, which is also worn with a black hooded cloak
- A Skywalker (Luke) had a son named Ben
- Han and Leia had a son named Jacen, who trained with Luke at his newly founded Jedi Academy and later fell to the dark side, just as Ben/Kylo Ren did. Also, he killed a family member (Mara Jade, Luke's wife, his aunt) to fully embrace the Dark Side
- Note that Jacen had a twin sister, Jaina, and there are some theories that Rey is Ben's sister
- Luke's original lightsaber being recovered from Cloud City and later passed on to others
You could also argue that there were more planet-destroying weapons in Legends, but I think that Starkiller base was more likely to be inspired by the Death Star in the films than by Legends.
Other plots, like Leia having a tumultuous relationship with New Republic leadership, occurred in Legends, but seem to me like they could easily be a coincidence, whereas the things above have an uncanny resemblance.
By the way, this is not a new thing, as all the movies have had Legends elements added to them (yes, even A New Hope via the Special Edition).