Euron Greyjoy made quite the impression in the Season 7 premiere of Game of Thrones.
He offered his armada to Cersei in return for her hand in marriage, which she declined. He left, vowing to return with a "priceless gift" to convince her to marry him.
We know from the Episode 3 description that Cersei will "return" a gift. It makes sense that it will be the one Euron gives her. Especially because it's highly unlikely she'll want to marry him, when she's finally obtained power in her own right.
But it will still be very interesting to see what Euron's gift will be – and what damage he might do to obtain it. Let's look at the options...
1. Tyrion Lannister
2. Ellaria Sand and/or the Sand Snakes
Ellaria murdered Cersei's daughter Myrcella with the help of the Sand Snakes. Before this, they sent Cersei a "gift" of their own – Myrcella's necklace in the jaws of a viper, a clear threat on the girl's life. The Sand Snakes may have allied with Dany right now, but they're not in the inner circle, so Euron probably has a better chance of capturing one or all of them than he does of getting near Tyrion. It would also make the line about Cersei returning a gift in Episode 3 fitting – perhaps it's not Euron's gift she returns, but the Sand Snakes'. Cersei is all about vengeance these days, after all.
3. Olenna Tyrell
5. Arya and/or Sansa Stark
Cersei has been after the Stark girls for a long time – Arya since she disappeared after Ned's beheading, and Sansa after she escaped King's Landing when Joffrey died. Cersei would especially value Sansa's death, considering she thinks she played a part in Joffrey's murder. But while Sansa warned Jon about how dangerous Cersei is in the premiere, it's unlikely Euron would ever get near her in Winterfell. Meanwhile, Arya is apparently on her way to King's Landing to kill Cersei, so her path could collide with his in some way. But no one thinks Arya is actually alive (except for those allies who know she is), so this doesn't seem super likely. And it wouldn't be a super satisfying way for either of the Stark girls to die at this point. But this is Game of Thrones, so it's not impossible.
6. A military victory
OK so we know from the Season 7 trailer there's going to be a huge sea battle, likely Euron Greyjoy vs Yara and Theon Greyjoy. Smashing Dany's fleet would certainly be a gift for Cersei, but if Euron does this before securing her hand in marriage, it doesn't give her a real incentive to accept his proposal. Also there's no way this really works with the whole "Cersei returns a gift" line.
7. Dragonbinder and/or a dragon
vote votesEllaria/Sand Snakes
vote votesArya or Sansa
vote votesOther (I'll explain in the comments)