As per the RBI guidelines, you can carry INR upto Rs. 25,000 only in cash while travelling abroad. Also, you run the risk of getting it exchanged at an expensive rate than in India. The other option you would have is you can use debit or credit card abroad but that would cost you anywhere between 3% to 5% more than a forex card. Therefore, exchanging INR to USD in America itself may not be a great idea.