Gama-chan is Naruto Uzumaki's toad shaped wallet. Naruto received Gama-chan when he was little, on one of his birthdays from an anonymous person. Gama-chan's presence and brief appearances in the series are used for comic relief. Naruto cares for "Gama-chan" and refers to it as if it were a pet, saying that it's happy when it's fat and full of money. He gets disappointed and indignant whenever Jiraiya's jaunts out for "research" would end up with Naruto broke, and Gama-chan emaciated.
When Tsunade made a bet with Naruto on whether he could master the Rasengan in a week, she took a money-filled Gama-chan as his part of the wager.