We were there two weeks ago and my sisters and their friend traded with a Jawa. I wasn't aware that they traded back items to other guests so I just took a couple of small, shiny items I found in my room (a tiny glittery bow ornament, a small craft mirror, a silver screw, etc.). The Jawa was happy to trade with them, and they all got droid parts. They definitely don't take any coins since another guest had his rejected. My sisters also tried to trade with the other Jawa that was there, but after checking all of his empty pockets, our binder clip was returned to us.
If you have some usable items, a toy car or a roll of tape, for example, definitely trade those instead! We saw some really cute interactions with both of those items!