From the official Goa tourism website:
"It is not permitted to take Indian currency out of India nor purchase the Rupee overseas. If you are arriving from a foreign country, you should change some of your currency into Rupees at the airport or at the nearest branch of State Bank of India where you are offered the best rates of exchange.
Money Exchange services are also available at most major hotels & resorts and private money changers in the area. Most reputed banks such as HDFC, ICICI etc also have ATMs that accept Master and Visa Card to withdraw cash.
Travellers cheques of all major brands are easily changed. The currencies that are most widely and easily accepted are the US dollar and British Pound Sterling."
http://www.goatourism.org/Travel_Kit/currency. htm
It's probably best to mainly use your debit and credit cards but to take some traveller's cheques (or a small amount of cash) as a back-up.
Chris