Treats
What works best for me is a 99cent loaf of store-brand bred. and tear small peices off, plenty of treats, little cost. You can also use scratch, anything that your chickens like in particular.
As for the clicker:
Train your chicken ,using this method. Click, give the chicken a treat,and repeat. The clicker is a handy tool if you're in a posistion that that you cant give the treat IMMEDIATELY, the chicken know's one is coming when he hears the click.