Certainly tell your card supplier where you are going as out of the ordinary purchases, especially cash withdrawals with be 'red flagged' for your safety!
Trace299 is correct with her information. Take some $TT with you to start you off. You really will have a problem using a card most places unless you are in the more tourist oriented Store Bay / Crown Point area., it is not that sort of society at all! Cash is still king! You should check with the owner of the establishment BEFORE you order to see if they can/will take your card. ATMs in the north, eg. Castara, Charlotteville, Roxborough do run out of cash and may not be refilled for several days. Always keep some cash in reserve, small bills in the safe. Take out what you need , $TT2-300 will do you for the day. USD are also taken at a street rate of 6-1.
Have photo id ( UK drivers license is good and easier to carry than your passport.),with you for using a foreign card