You have to get there by a vessel...there is no place on the island to park, it is a nature preserve. If you have a kayak or canoe you can park at public launch site just before Fort De Soto park entrance and kayak out.
Shell Key is only accessible by boat. There are a few places that you can drive to and kayak over to the island if the water is calm, but you will likely have to contend with alot of power and sailing boat traffic across either North Pass-A-Grille Channel or Bunces Pass from the south side. There is a ferry service from Pass-a-Grille Beach that takes you over there, but you can't stay overnight.
The Ft DeSoto boat ramp allows overnight parking
Thanks! Your answer is awaiting moderation.