Re: Sanibel Island, Ding Darling
Redfish and snook will hit many types of flies, from spun-deerhair monstrosities to subtle, almost dainty flies like a white DT. Study the tide charts since they will have a profound impact on your fishing. Higher, moving tides are good for backcountry shorelines since so much of that area becomes unfishable on a low (including the flats and shorelines deep inside the park area). On a low or falling tide look for moving water near cuts or deeper flats. The redfish up there (and snook, to an extent) can be found across a much broader area than many other spots since the turtlegrass flats are so extensive. Your yak is a perfect way to find them.
As an alternative to Ding Darling you can put in at the ramp in Matlacha which gives you access to a host of other quality backcountry spots. Bear a gradual right when leaving the ramp and across the bay to fish the long shorelines on the far side or go left under the Bascule Bridge and fish along the long shorelines on the right side of the channel. When fishing open flats consider a fly that makes some noise like a Gurgler. Your best fishing will happen early and late in the day. If you are up to it you can also fish the dock lights around Pineland and especially Bokeelia at night. It's a wonderful place that harkens back to the old Florida I remember and pine for.
Good luck and enjoy.