In Return of the Jedi, after escaping from Jabba's Sail-Barge, R2-D2 land in the Tatooine sand. Luke and the others pick them up with the skiff's magnets.
Why did Jabba's skiffs have magnets in the first place?
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The brand new (and fully Disney canon) junior novelisation for the film describes them as "Cargo magnets".
“We’re on our way!” yells Lando, stepping over a dead guard to get to the controls.
Moments later he is lowering the skiff’s cargo-magnets to pull the droids out of a sand dune.
And then they’re away, zooming across the dunes to safety! A final explosion erupts behind them as the sail barge—and a great deal of evil—disappears in a massive fireball.
Since the skiffs are described (by the old Star Wars Encyclopedia) as being used for transporting cargo, it makes good sense that they'd have a way of loading and unloading the skiff without having to make a landing.
A repulsorlift utility vehicle, it was usually used to move cargo or passengers. Tatooine crime lord Jabba the Hutt used a number of skiffs as escorts for his sail barge. His henchmen often rushed to a raiding site in skiffs while barge passengers enjoyed the battle from a safe distance.
A skiff deck was completely open, with a control station for the driver and sometimes a labor droid at the rear. One repulsorlift engine provided forward thrust; the craft was maneu-vered with two steering vanes hanging off the back of the hull. A skiff could hold more than 100 tons of cargo and reach speeds of 250 ki-lometers an hour and heights of as much as 50 meters above the surface. When fitted with up to 16 seats, skiffs were used as mass transit vehicles on poorer worlds.
It does have an answer in EU - Legends
These skiffs are the Ubrikkan Industries Bantha-II Cargo Skiff as named in The Star Wars Sourcebook, Cracken's Rebel Guide and Galaxy Guide 7: Mos Eisley
As a cargo skiff many varients of the Batha-II
were equipped with retractable magnetic lifters and loading ramps for transporting cargo onto the skiffs deck