Hi Joy,
The currency in America is the US Dollar, which is widely available in the UK. Widely accepted are US Dollar cheques; Pound Sterling traveller's cheques are rarely accepted and few banks will honour them. Change is issued in US Dollars. One or two items of identification (passport, credit card, driving licence) will be required.
Most major credit cards are accepted throughout North America including American Express, Diners Club, MasterCard and Visa. Visitors are advised to carry at least one major credit card, as it is common to request prepayment or a credit card imprint for hotel rooms and car hire, even when final payment is not by credit card.
I hope this helps.
Kindest regards,
Monty