If you are travelling to USA, you must carry your major part of currency in a forex card. Forex cards are considered the safest way to carry foreign currency. They are just like prepaid VISA/Mastercard cards which can contain a single currency or even multiple currencies in case you are looking to travel to some other country other than the US.
It's advised to carry 70% of your total amount in a forex card and the rest 30% in cash which can be used to pay for small expenses. You should also carry a spare forex card in case you lose one somehow.