When peeta hides in the hunger games , what does he eat ?

There was fresh water available, fish, and plants. He was so sick, that he wasn't very hungry though. You can't go long without water, but you can last days without food. He also had plenty of berries to eat, since he used them as part of his disguise.

He eats himself!
LOL, just kidding.

He was near a pond so he most likely ate fish and drank the water.