They seem to access value in trades, which makes sense. Saw a lady give one a park map and she got back a crumpled napkin ... park maps aren't hard to come by.
Jawas like shiny. My DS traded them giant gold buttons and jingle bells, they loved it and they seemed to spend more time with him. Another great item is gold mardi gras beads. They are cheap and easy to carry around. Think shiny!