Hanging out on the beach, drinking and eating is what everyone does best in Belize. You will love it, promise.
As for shopping, it's very limited. At least, that's been my finding, and I love to shop, too. I just leave the shopping for the other travel places, and enjoy everything else the Isla Bonita has to offer.
We stayed at Capt. Morgans the first time we came to Belize, and it's very nice, but far away from town. They have a boat that will take you back and forth to town, so if you enjoy the boat, then this is a good choice. You have to schedule the trips. They also rent golf carts, and that's what we ended up doing. The accomodations and restaraunt are great there. Enjoy...I know you will.