(I mean, come on, everyone is making a list. Why can't I?)
Oh, and there will be spoilers so read at your own risk.
1. Caf is cannon. It is mentioned only once in the book (the advantage of having an e-reader like a Kindle is that you can search the book easily), but the infamous beverage of the old EU is now part of the new EU.
2. Han and Chewie are taking an awfully big risk. Like the last trailer for The Force Awakens, Luke and Leia are mentioned, but the only member of the Big Three that has dialog in the book is Han. While on a scouting mission for the New Republic, Han and Chewie learn that the Imperial presence on the Wookiee homeworld of Kashyyyk is, for a very brief time, going to dip significantly. "The details are fuzzy," their source tells them, but the opportunity to free the Wookiee-world lights a fire in Han's belly. Making promises he may not be able to keep he calls in every favor he's got, abandoning his responsibility to the New Republic, to free Kashyyyk.
This, in my opinion, whether successful or not, will definitely be mentioned in The Force Awakens.
3. Boba Fett may still be dead, or... ...he may still be alive. A miner and a "sheriff" find a heavily damaged set of Mandalorian armor while shopping in a Jawa sandcrawler. The sheriff, who by all indications isn't Boba Fett, decides to take the armor for himself, sending the miner limping back to his bosses empty-handed.
How the Jawa's got their hands on Fett's armor is anyone's guess, but to para-phrase Lucasfilm's Pablo Hidalgo, Boba Fett is still in the Sarlacc pit until a good story pulls him out.
4. Another member of Gold Squadron has been identified. Remember Tycho Celchu from the old EU? He was supposed to be the A-wing pilot who split-off from the attack force to lead TIE fighters away from Lando and Wedge. That A-wing was followed by a Y-wing piloted by the book's lead character, Norra Wexley.
5. Wedge Antilles was a friend of Ahsoka Tano. To quote the book: "Once upon a time, he crashed an A-wing at the lip of a volcano--one of his first runs out as a pilot for the then-burgeoning Rebel Alliance, at the urging of a friend--a rebel agent known only as Fulcrum."
Of the few lists I've seen about "Aftermath" this is something that hasn't been mentioned, although several of Kindle readers have highlighted it as an important passage. The only things I can take from this is that Wedge might be a couple of years older than Luke, and that Ahsoka survives deep into the length of the Rebels TV-series. It's not much, it may just be grasping at straws, but it's nice to see that Ahsoka had an influence on the Classic Trilogy.
From a certain point of view.
6. Even minor Clone Wars characters have significance. Remember Cut Lawquane? You gotta go way back to season two and the tenth episode which was called "The Deserter." While the fall of the Empire tears two brothers apart, their father mentions Cut and that, "He saw the truth of things: No side in war is the right side."
Another small character from the Clone Wars (appearing in five episodes) was the bounty hunter Sugi, who was the aunt of bounty hunter Jas Emeri, another major character in "Aftermath."
7. Dengar is still alive. Whether he'll be around 30 years later is anyone's guess, but he has a scene with a young man calling himself Mercurial Swift. It's during one of several Interlude chapters seemingly unrelated to the main story, but this scene seems to have less impact than the rest. The only thing I can take from it is that we may hear from Swifty in The Force Awakens.
8. Orphans are another product of the war machine. Like Luke and Leia before them, children are the misplaced casualties of war. One Interlude scene on Naboo involves small children lining up to be examined a picked over for possible adoption, another involves young students being shipped off to an Imperial academy only to discover that the academy has just been liberated by the Rebels. These children have few options. While some of the students can return home, others can't, the academy being their own way out of their old life. They could join the New Republic academy, or they could just go on their way. Neither option seems right. For the youngest.... Well, some were members of the Anklebiter Brigade on Coruscant, fighting against the Imperials as the Empire fell. Some felt like they had purpose back then, so, if they're not adopted or if they runaway maybe they can feel useful once more.
In short, look for a man in his late 30's named Iggs in The Force Awakens.
9. Mister Bones! In all seriousness, I don't think he will have any impact on The Force Awakens, but he is by far the coolest battle droid you've ever seen, and the only character in the book to say, "I have a bad feeling about this!"
10. Lando wants Cloud City back. Another Interlude scene, it appears that Lando, with Lobot's help, has hired a team of pirates/bounty hunters to help take the city back from a Goveror Adelhard. This may have more to do with the mobile-game, Uprising, than the new movie, but it is another cool thing to learn that Lando has plans of his own to fight the floundering Empire.
11. If there is a bright center of the universe... ...Jakku is nowhere near it. It is a dead place. Some mining, but nothing else. If you want to escape war and drown yourself in Knockback Nectar like Corwin Ballast, Jakku is the place to be. "Wanted to take [my family] as far away from the fighting as I could," he tells the bartender. "A place where the war will never find us. The farthest-flung nowhere rock I could find on a star map."
"Well, you found it buddy," the bartender tells him. "You don't get more nowhere than here. War ain't got no reason to roll up on this rock."
Earlier in the conversation, the bartender mentions a rumor of kesium gas wells going up near a place called Cratertown. I don't know how significant kesium gas is, but that may be a resource a desperate military force could use.
12. Is there a mysterious puppet-master at work? The New Republic is getting important information from a spy known only as The Operative, but is that the same mysterious figure currently commanding the Empire's surviving Super Star Destroyer? Is it the future Supreme Leader of the First Order, Snoke? Or could this fleet admiral be, dare I say it, Thrawn?