Prepare both boxes of vanilla pudding according to the package directions, using an electric mixer. Blend the cream cheese into the pudding, mixing thoroughly to remove any lumps. Fold the whipped cream into the cream cheese-pudding mixture.
Spread a third of the graham cracker crumbs into an even layer in a low-sided clear bowl. Pour half of the pudding over the crumbs and spread until it reaches the sides of the bowl using an offset spatula. Repeat this process once, setting the remaining third of the graham cracker crumbs aside. Cover with plastic wrap pressed directly against the surface of the pudding and chill in the refrigerator for at least 2 hours.
Remove and discard the plastic wrap. Following the edge of the bowl, create a 1 1/2-inch border of blue sparkle gel around the edge of of the pudding. Use a small offset spatula to gently spread the blue sparkle gel, creating the look and texture of ocean waves. Cover the remaining exposed pudding by piling the reserved graham cracker crumbs on top, mounding in the center, to resemble an island in the ocean.
Cut the sour candy belts into small rectangles to resemble beach towels and place them around the cake with the bear crackers on top of each one. Place a few bear crackers inside peach candy rings (to look like inner tubes) and place them in the blue sparkle gel so that they appear to be bobbing in the water.
To make the palm trees: Insert a mint stem into each wafer cookie, pushing down until the leaves meet the top of the cookie. Gently press into the center of the graham cracker crumb island.
To make the candy crab: Use scissors to snip a small triangle out of the rounded side of a cherry slice, positioning it close to the flat side, to look like a claw. Snip a small notch out of the opposite side along the curve, to fashion the arm that the claw is attached to. Repeat this process with a second cherry slice. Insert a toothpick lengthwise into each arm and set aside. Prepare the crab body by holding the rounded sides of 2 cherry slices together back to back. Secure together using 2 toothpicks, being sure to push the toothpicks deep enough so they are only exposed on top. To make the eyes, use a dab of blue sparkle gel to attach an eyeball to the bottom of each gumdrop. Secure the gumdrops on the toothpicks sticking out of the crab body. Push the claw toothpicks into the sides of the crab body. Bury the bottom half of the crab body in the graham cracker crumb sand.
Sprinkle the island with sanding sugars where the ocean meets the graham cracker crumbs. Refrigerate until ready to serve.