Get a post office cash card, you load it with cash and use it as a debit or atm card, low charges, there is no credit so you only spend what you have and they will replace it if it is lost or stolen.
You can get one from the post office or over the internet
Travellers cheques are secure (you make a note of the numbers and if you lose them you can report them stolen and get the money back). Buy at a travel agent.
Some tourist areas (like Florida) will even take them as "cash" and give you change.
Your debit card will work over there, so you can take out dollars from the hole in the wall (check with your bank that you can use it in the US first).
Also of course credit cards can be used to save carrying cash. Credit cards are used a LOT over there.
DONT take money out the hole in the wall with your CREDIT card as you start paying interest as soon as you withdraw the money.
Almost every place here in the USA will take Visa or Mastercard - either as a credit or debit card - even Wal-mart. And we have a zillion bank "holes in the walls" to get cash out of them. You can check with your bank to see which of our banks take your cash card.
I'd definitely take some travellers cheques as it is so easy to get new ones if your others are lost or stolen. Not so easy if you are relying on debit/credit cards.