1.Galen Erso and his family can be seen drinking blue milk. Blue milk also makes an appearance in Star Wars: A New Hope and Star Wars: Attack of the Clones.
2.Galen Erso shares a name with Galen Marek, the protagonist of The Force Unleashed series of video games.
3.Saw Gerrera, played by Forest Whitaker, makes his first appearance as a young man in Star Wars: The Clone Wars as an animated character.
4.Likewise, in the Rebellion headquarters, an announcement can be heard for a General Syndulla, which is probably meant to be an older (and more decorated) Hera Syndulla from Star Wars: Rebels.
5.Her ship, the Ghost, may even be among the rebel fleet over Scarif...
6....and her Astromech droid friend Chopper can also be seen briefly at the rebel base.
7.While running through the list of special weapons, Jyn Erso and Cassian come across a project called “Black Saber.”
8.The orange-sided AT-AT walkers on Scarif are actually AT-ACT walkers, or All Terrain Armored Cargo Transports.
9.While on Jedha, Jyn and Cassian bump into two familiar characters in the crowd.
10.The planet Yavin 4 should be familiar to anyone who has seen the original trilogy, as it’s the main base of operations for the Rebel Alliance in Star Wars: A New Hope as well.
11.R2-D2 and C-3PO also make a brief appearance in the rebel base on Yavin 4.
12.The transport carrying Jyn and the other prisoners on Wobani is a HAVw A6 Juggernaut. It makes its first appearance in Star Wars Episode III: Revenge of the Sith.
13.Chirrut Imwe and Baze Malbus are "Guardians of the Whills," a longstanding fixture in Lucas lore.
14.The Hammerhead Corvette used to push the disabled Star Destroyer into another ship is probably related to the Hammerhead-class cruiser, which was first introduced in the video game Star Wars: Knights of the Old Republic.
15.The people at Saw Gerrera's base can be seen playing a rudimentary version of Dejarik, the holographic game that Chewbacca and C-3PO play in New Hope and that Finn briefly encounters during Force Awakens.
16.During the Battle of Scarif, Cadet Pedrin Gaul (Red Five) is killed, making room on the roster for Luke Skywalker in Star Wars: A New Hope.
17.Darth Vader's lair (Bast Castle) in Rogue One: A Star Wars Story is based on original concept art created by Ralph McQuarrie for Empire Strikes Back.
18.After the Rebel Alliance council meeting, there is a call over the intercom for a Captain Antilles.
19.Aboard the Tantive IV, you can also hear someone mention that the escape pods need to be checked before the ship flees Darth Vader.
20.K-2SO nearly delivers the iconic line, "I have a bad feeling about this," but he is cut off before he can finish.
21.On Scarif, two stormtroopers can be overheard talking about the "T-15 model" being discontinued.
... which mirrors a strikingly similar conversation between two stormtroopers in A New Hope.
22.This is the 4th Star Wars movie Warwick Davis has played a part in.
23.In Rogue One, the Wilhelm Scream can be heard as a stormtrooper is killed.
24.The interior shots of the Citadel on Scarif were actually filmed in Canary Wharf station in London.
25.The clamps used to retrieve the data file in the Citadel are similar to the clamps used by the protagonist of Lucas's first film, THX 1138.
26.Many of the new stormtrooper helmets in Rogue One have been seen before, in the Poe Dameron comic book.
27.Darth Vader can be seen in a bacta tank, the same kind that Luke is put in to heal after the Wampa attack on Hoth.
And nobody looks good in a bacta tank. Some things never change.