Luckily there's no shortage of sand to begin your search. Sanibel and Captiva have more than 15 miles of combined public beaches, although according to island experts, it's not about where you go shelling but when you go.
For the best chances of uncovering a rare find--like the brown-spotted junonia or a scallop-shaped lion's paw--head to the beach at low tide when a greater portion of the shoreline is visible. Also, consider hitting the beach after a storm when the winds and waves disrupt sand beds and unveil shells that were previously buried.
Try your luck on Lighthouse Beach--on the eastern tip of Sanibel, it's where you'll also find the island's sole lighthouse. And for a closer look at area shells, check out The Bailey-Matthews Shell Museum where one-third of its exhibitions are dedicated to varieties found on Sanibel and Captiva.
Finally, if you still can't find the perfect island souvenir, buy your favorite at She Sells Sea Shells, above, a shell shop where you'll be shell-shocked at the amount of shells it sells. How's that for a tongue twister?