Our son did a 6month trip from NC to Bahamas and back in '05-'06 on his 27' Watkins sloop, Walkabout. I helped him with the provisioning plan and some tests of food quality and storage techniques. He left with 8 months provisions for the 6 month trip. His take was that other than rum, grits and frozen lamb everything was more expensive than the states. The rum in the Bahamas is better and less expensive so wait till you get there. A good site for high quality dehydrated and canned food at good prices is http://www.internet-grocer.net/product.html
Taking food with you is important for independence and self reliance. about 40 cruising boats, power and sail , were held up in Chubb Cay for a month because of stronger than usual prevailing easterly trade winds. Chubb Cay had been leveled in the two prior hurricane seasons and there was no food, water or fuel of any kind available. The cruisers had planned to re provision at Chubb and were running our of everything. Our son and his crewman shared two 35lb fish they caught with other boats when they first got there and fished during the 5 days he waited for the winds to change. One captain was so greatful for the fish that he gave Andre one of his spare alternators to replace the one on Walkabout that had crapped out (brand new from The Evil Empire 4 weeks earlier!). 2 months provisions is a minimum IMHO. Conversley, water was free in George Town at the dinghy dock. Carry as much water as you can, in jerry cans on deck if necessary, it never rained where he was during the whole trip.
Dehydrated food lasts almost indefinitely. Canned foods can rust and he discovered that putting cans in a zip lock didn't prevent rust because the cans chafed through, hard side Rubbermaid type boxes work better. Zip locks worked for all the dehydrated though. He had an Engel MT35 portable freezer about the size of a 35 qt ice chest. He made ice, kept a few pints of ice cream, and froze fish he caught, after filleting, in zip locks. Wax encased cheeses lasted 6 months or more canned cheese was good.
Easiest meals using least fuel making least heat were instant oat meal in assorted flavors, instant grits, instant mashed potatoes (see internet-grocer dot net, granuals are better than the flakes), also Idahoan brand instant mashed potatoes in various flavors, Lipton flavored noodles in foil packages, Knorr soups and noodle dishes, various gravy mixes to flavor the above. He preferred meal size canned beans over dried for speed, fuel and heat reasons. Dried fruits of all kinds, home made turkey jerky (cut boned turkey breast 1/4 in. thick or less, 50/50 Tamari or soy sauce and water soak 24 hours, spread on cake racks on cookie sheets and dry in oven 140 degrees max;or 25/75 Real-Lemon juice/water and salt same drying process).
He used about 1 gal alcohol/month in his unpressurized Origo 2 burner stove and about 1lb/ month of propane in the Magma grill.
His cost for food and booze (forget the beer too expensive although you can bring some to trade locals for lobster and conch) $450/month