My players are going to be transporting a person out of Iziz on Onderon. The job itself is kind of a throwaway (the captain just needed an in world reason as an excuse to agree to go there), but I'd like to flesh it out a little bit and maybe even surprise them with something real.

At this time, Onderon is controlled by the Empire. My players are currently a crew of EotE characters coming off a successful heist of the Jewel of Yavin. They will be making the transition to working with the Rebels soon, mostly likely eventually actually joining up. The crew is generally "good," as far as EotE characters go; no needless violence, no kleptomania, generally try to be helpful when they can.

That's probably enough info to go on. No wrong answers here. I'm just hoping to gather some ideas from outside perspective.

I'll share a godsend, the 21 plots series:

https://www.drivethrurpg.com/browse.php?keywords=21+plots&x=0&y=0&author=&artist=&pfrom=&pto=

Sure, they're for the Traveller game, but they are easily converted, and give lots of nifty NPCs, motivations, etc.

Rebel refugees or rebel fighters/stranded strike team in need of extraction might be a good way to hook them into the rebellion.

Rebel fighters/stranded strike team outline: they are approached by a rather average looking person who asks them if they can discretely transport X number of people off-world, assuming the players say yes, when they go to pick their passengers up they find them in a firefight with the imperials, who fire on the party as well, seeing them as accomplices. They then extract the rebels and escape.

Refugees outline: They are approached by a rather furtive person who rather desperately offers the party a rather small sum, claiming it is all they have, and asks the party to help get them and/or a group of others off-world, and, if pressed, reveals that they are trying to escape the Empire for X reason(s). the PCs then have to smuggle them past the Imperials and reach a rebel safe-haven or rendezvous of some kind.

Or, as I reread your OP and thought I might have misunderstood somewhat, they are contacted off-world and requested to extract the aforementioned rebels/rebel refugees in a manner similar to my original proposal.

In Mr & Mrs Smith (the movie), the prisoner was a fake prisoner just to get the two characters together so they could be ambushed. The prisoner was built up to be some hardened terrorist (The Viper, or something like that) but was just an incompetent low-level corp employee. He cracked easily when pressed.

I like that aspect over the old "important prisoner" trope we so often get. The (your) captain could just of hired this guy to be a prisoner so he could get the ship where he needs it to go. Harmless enough. The guy's an actor who wanted to go to Onderon anyways. Made a deal to act like a prisoner for free spacefare. Later, the PC's could see this guy walking down the street, working a taco stand, or boarding a ship. Then it might get crazy because they think he escaped! The captain tries to persuade them away from pursuing it, saying it's not the guy, but the PC's are sure of it. All kinds of craziness can follow!

Thanks for the replies. I'm just going to post what I decided to go with in case anyone ever stumbles on this in the future. I'm going to use the passenger as a way to create an adventure hook down the road.

Specifically, the passenger will be Ashur Sungazer from the FaD core rulebook adventure. I'll have him make a connection with the scholar of the ship which will give me an excuse to reach out with him when I want to run that adventure.