Do not leave anything in your car, theft is frequent. Be careful where you park in Port of Spain, police are diligent and will tow the car away. Best to make reservations in advance. Several companies do not accept credit cards, but require a considerable cash deposit. Deposit varies from company to company, as does method of payment, book in advance.
Many companies have offices at the airport.
Some companies only rent for a minimum of 3 days. Econo Car Rentals, 191-193 Western Main Rd, T6228072, one of the cheapest. Peter Gremli Car Rental, Crown Point, T6398400. Thrifty Car Rental, Turtle Beach Hotel, T6398111 and other agencies. On Tobago, bike repairs and parts at Numeral Uno hardware store in Carnbee, a good contact for joining local riders for some fun road riding.