One of the first things you'll need to do when you get to the United States is to open a bank account. A bank account is necessary in order to manage money, make deposits, transfer funds and use a debit card. Keep in mind that some vendors might charge extra fees for or not even accept non-US cards.
In the US it is considered extremely unsafe to keep large sums of cash at home. Using a debit card is more practical than cash for the majority of your everyday transactions.