Gama-chan (ガマちゃん, Gama-chan, English TV: Froggy, Literally meaning: Toad-chan) is Naruto Uzumaki's toad shaped wallet. 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.
On the underside of Gama-chan, a white strip can be seen. The strip roughly says Naruto's Wallet (なるとさいふ, Naruto Saifu).
It might be based on the Chan Chu, the Lucky Money Toad, a Chinese symbol of prosperity depicted as a frog sitting on top of a pile of coins with a coin in its mouth.
The Japanese word for frog, "kaeru", is a homonym that means "return / to return". It is considered lucky in Japanese culture to keep a frog in wallets (in whatever form, whether as figurines or keychains, etc.) for money to come back when it is spent.
The creator of Naruto, Masashi Kishimoto, says "One day, the following incident took place. I got stuck writing a manga just before the deadline, so I lay down behind my desk to take a short nap. When I was looking for something to use as a pillow, I found a big frog-shaped gamaguchi cushion. (This is a cushion modelled on the froggie wallet that Naruto uses in the series, it was made as a present for readers.)"