Little boys will love the idea of working like daddy in the garage and everyone will appreciate the fine motor workout you can get from matching nuts and bolts. This idea (and several more in the same post) from Counting Coconuts.
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