Collectible investments are physical objects and tangible assets that have the potential to increase their value and diversify your investment portfolio. Collectibles can be anything that anyone collects, but some categories offer reliable returns, such as stamps, coins, toys, works of art and sneakers. Common categories of collectibles include antiques, toys, coins, comics and stamps. People who accumulate collectibles take a long time to pick them up and usually store them in places where they won't be ruined.