Shiny is the key! Some fake jewels, arcade coins, glow sticks/toys, pens/pins, etc. You can probably clean out the bottom of the toy chest or junk drawer and find plenty of items. Even things like old Happy Meal toys could be seen as "valuable". Keep in mind that some Jawas will trade and some will not. You may ask their handler if the Jawas are trading today before letting the kiddos approach them so they aren't too disappointed if the Jawa won't trade.