Grenada uses Eastern Caribbean Dollars (XCD), allso called EC Dollars here. US dollars are fine, credit cards are accepted in bigger shops & very few restaurants in the north, but more in the south. Our closest restaurant, Aggie’s, is cash only, for example, and you might be able to use a card in a larger gas station. We always found it wise to withdraw some local cash from the bank machine or change some Canadian, US or British Pounds Sterling cash at the bank (you’ll need ID) so you can buy little things like beer or chicken & chips on the beach. Most people are happy to accept US which is generally at 2.72 EC per 1 US dollar.
Tip: You absolutely must tell your bank and credit card company that you are travelling to Grenada or they will block your cards for fraud protection due to unusual spending!