Elf house on a tree! That would be cute in the garden, especially in the tree over grown with ivy. How about some battery tea lights in the windows during outdoor parties. I hear the fairies/elves whispering "home school project" in my ear.
Put a picture of the beach you visited in a shadow box frame and fill the bottom with sand from that beach. Much neater than a random jar of sand and shells! decorate the frame or put seashells or treasures found on the beach in the shadow box