As you get off the ship, there is a "mall" where you can buy some of the things you mentioned. You'll be docked right in Fort de France; the La Samane Park, which you can see from the ship, has "vendors" where we found everything we wanted to buy.
But . . . I think it would be a shame to go to Martinique and not see anything. I'd like to recommend a wonderful, knowledgeable tour guide, Kleber, who is a charming and sophisticated gentleman with an immaculate Mercedes. He took us around to see the Balata Cathedral [replica of Montmartre], a rum factory that was gorgeous, the ruins of St. Pierre, the Gauguin Museum, and then drove along the beach back to Fort de France. I don't know how much you can reasonably do in the time you have, but if you email him and tell him your time frame, he will be able to help you. He can also tell you where to buy the souvenirs you wish. His email address is firstname.lastname@example.org - he will be able to hel.