Not sure how people would feel about a cake that isn't made of cake, but it's still neat. (One of the commenters suggests using large pieces of watermelon to hold all of the other fruit, which sounds more appetizing.)
Watermelon salad... genius! Don't know what is in these, but watermelon and feta salad would work. Also done with cucumbers and salmon or salmon mousse.
fruit pizza 1 (18-ounce) package refrigerated cookie dough 1 (8-ounce) package cream cheese, room temperature 1/3 cup sugar 1/2 teaspoon vanilla extract or other flavoring (almond, orange, or lemon) Fresh blueberries, banana slices, mandarin orange sections, seedless grapes, strawberry halves, kiwifruit (or any other 1/2 cup orange, peach, or apricot preserves 1 Tablespoon water