Old font/type boxes make wonderful shadow boxes! You can find them on Etsy and at some antique and second-hand shops. As times go, fill the slots with little memories.
Here: A 45-year-old stuffed mouse from a childhood collection, a spray case with herbal remedy, a stone collection from a museum, a note from a friend, two images of my daughter, a miniature horoscope book.
Ideas: Tickets to a show, old passport photos, school pictures, jewelry, broken watches, bottle caps, stickers, oils and ointments, stones and crystals, coins, stamps, art objects, small bottles, miniature books and boxes, folded notes, dried flowers, ribbons and buttons.