Again Qui-Gon and Obi-Wan split up for, in the movie, no readily apparent reason. The ship has a contingent of the Naboo Royal Guard to look after it, and nobody's going to come raiding it anyway. About the only thing that does make sense is if there are indeed giant sand creatures floating around on some wandering monster table somewhere.

Random Encounters: Tatooine, desert

01-93 Nothing
94 Bantha
95 Jawa
96 3d10 Jawas
97 Sand Person
98 2d8 Sand People
99 2d8 Sand People, with Banthas
00 Giant Sand Creature (refer to Giant Sand Creatures subtable)

Transcript

Qui-Gon: We all head into town in search of weapons for the ship.
Obi-Wan: There's no need for R2-D2 to go into the town.
R2-D2: And your skill in Armoury is...? How about Power Engineering? Welding?
Qui-Gon: He's right. We need him to spec weapon stats.
Obi-Wan: Fine. I'll stay on the ship and enjoy the air-conditioning.
Qui-Gon: We can't split up!
GM: Thank you.
Qui-Gon: There's no XP to be earned sitting in the ship!
Obi-Wan: We're charged with guarding the Queen.
R2-D2: {aside} By the end of the day, I hope to be charged with Drunk and Disorderly.
Obi-Wan: The ship could get attacked by giant... sand creatures. Random encounters aren't just going to stop if we all go into the town.
Qui-Gon: Hmm. Good point.
GM: <sigh> Split up then. I guess I'm buying the "Giant Sand Creatures" supplement after all.