All sorts of things can fall off the back of a ship... or truck, or wagon, or whatever. People move goods around a lot, and wherever people are moving goods by vehicle, something can fall off. That doesn't necessarily make the goods shoddy or cheap. If you're lucky you might find a real windfall this way.
For an adventure idea, consider having the party run across a load of cargo somewhere. It's fairly obviously fallen off the back of something, and the cargo carrier didn't notice and has vanished into the distance. It could be lying on a road, or a less travelled path through a forest, or maybe floating on the sea or washed up on a beach.
Once the heroes have found the cargo, they need to decided what to do with it. They might just want to claim it for themselves and perhaps try to make some money by selling it. Complications: the person they attempt to sell it to recognises the cargo and questions how the heroes came across it. The alternative option is that heroes may feel obliged to try to return the cargo to its rightful owner, which can trigger a quest to track down who that is.
Perhaps the cargo is contraband. Perhaps it contains information - title deeds, bank ledgers, business plans, diplomatic communiques - and maybe something in there is highly incriminating. Maybe someone you don't want to cross is desperate to get it back.
Something falling off the back of a vehicle can lead to a myriad of different adventures!
Commentary by Keybounce (who has not seen the movie)
So how does stealing someone's identity really work? Is it effective if you just call yourself by name X, without actually having studied that person, and not knowing anything about them?
And why do I get the feeling that this Xasha was seen in-comic some many, many years back, perhaps in a scene that had been commented on by many people as a "Whatever happened to this shape-changing bounty hunter?" Wait a sec - how do we know that person is a shape changer anyways? "They look different now" isn't the answer. Did you see them change form? This "Xasha" sure looks different, but... is it the same person? No. Yet it's claiming to be a shape changer.
What have we seen of shape changers? They don't seem too bright. Different versions might not have exactly the same memories of everything. What if every "shape changer" is really just a serial identity thief?
Naah, that would make more sense than the original movies, that can't be true :-)
Commentary by memnarch (who has not seen the movie)
Oh. Ohhhh dear. No way that's just parts falling off. On the plus side, the previous Xasha is probably dead judging by the previous Han Solo. On the minus side, this is probably someone tracking down that Xasha or the killer of that Xasha. Or if that Xasha isn't dead, then they've probably just caught up for some revenge. If this is where things end up going, I foresee sepia and grey flashback panels in our future again.
Hmmm. This would also mean that someone or something has already boarded the wyrm-ship that Chewbacca and Xasha arrived in and is starting to strip that ship for parts. Could be that the First Order did notice the tractor beam and is actively boarding or attacking the ship. They would have had to have immediately noticed the action and come running though, so that's still less likely than "surprise mercenary", if only slightly.
As for most of the parts falling off the back of a ship, I'm hardly surprised. I think I remember seeing comments back during the rescue of Princess Leia that it was the equivalent of seeing a falling apart Ford Model T used for a getaway vehicle. To have an original, still working vehicle that old, it would need to be practically never used. Otherwise you'll end up running into the Ship of Theseus problem where the Millennium Falcon may or may not be the original ship anymore and have tons of quirks to work around. With how long Chewbacca spent repairing the ship for Han in the Original Trilogy Episodes, I bet he'd have the best chance of fixing anything on the Falcon (including the modulator) with those circumstance bonuses versus Rey's flat Repair rank.
Transcript
Rey: So... you’re Xasha now?
Xasha: Yeah, I stole the identity of some bounty hunter.
Chewbacca: She used to work for Boba Fett, helping him track down Obi-Wan.
[SFX]: thump
Finn: Boba Fett? Who’s Boba Fett? And Obi-Wan?
[SFX]: clang... clang...
BB-8: What’s that noise?
GM: Hard to localise. It might be inside the ship, or out in the docking bay.
Rey: Probably bits falling off the Falcon.
Xasha: We better go take a look. {runs out}
Chewbacca: I think most bits of the Falcon originally fell off the back of a ship.
Rey: Yeah, itself.