What do Chickens eat?

Chickens eat lots of different things.  
When chicks are first born, they don't eat anything the first day.   When they are fully fluffy and a day old, they start eating chick starter.  Some people use Organic and some people use medicated chick started.  
When the chicks are old enough to go outside they can eat chick feed, bugs, worms, and vegetables.   
It is good to feed your chickens crushed egg shells to help make their eggs hard.  
If you have free range chickens, your dog might chase after them and kill them and eat them.  If they are free ranging, they eat lots of bugs out of the yard.  They eat ticks.  At night they will go  back to their nesting box for the night to lay their eggs. 
If you keep your chickens in a pen, you can still let them eat bugs and worms.  They also like almost anything you give them.  They will eat grapes, orange peels, table scrapes and even pieces of cooked chicken.  In the fall, they love pumpkins.   If you give your chickens onions they will taste like onion eggs.  
For treats you could give them Happy Hen Treats.   Here is a link where you can buy them. 
http://www.happyhentreats.com/qswzcijbp2nip3ns03vhz078gunkqc

You can also make your own treats by putting pieces of fruit, meal worms and other yummy things in ice cube trays filled with water and freezing them.  Give them one cube to peck at.  This gives them water and treats and gives them something to do.