Yeah, ATM once you get here. Find out what your bank charges for international debit card use (if anything); if it's a big, unavoidable fee just withdraw a big amount once.
In a pinch, many hospitality/tourism-focused businesses will take U.S. cash. You won't get a great exchange rate on it, but it's widely-accepted currency.
If you think you'll be tipping (baggage handlers, drivers, hotel staff), bring a whole bunch of U.S. $1 bills in good condition for that. Our smallest denomination bill is $5, so if I'm tipping anything less than that it's coins, and I always feel like kind of a tool slipping someone coins (bulky to carry, too.)
Hope you enjoy your holiday! :-)