I'm a Captiva resident and Captiva has some of the best shelling around as less tourists come up here than Sanibel. The best public beach on Captiva is Blind Pass, park south of the bridge as parking is more readibly available than the north end. There isn't much public access on Captiva as many of the beaches are private. Another beach on Captiva is at the most northern end just past South Seas but parking is limited. Another nice beach that you must attend is by the Sanibel lighthouse. Nice walking area with a fishing pier and nature walk but not as many shells.
For restaurants I would pick Island Cow for dinner, especially when there is a live singer and Doc Ford's down on rabbit road. There are many restaurants to pick from and all are unique in their style.
For places to stay it varies on price. Captiva, Tween Waters and South Seas, remember South Seas did just re-open but is still very limited in their offerings and very expensive. On Sanibel I would check Sanibel Inn or any of the motels they own. Check
SanibelInn.com and there will be links for all there motels.
Your best bet will be to check
Traveladvisor.com and read reviews but take them with a grain of salt. SouthWest, FLA can be hot, there are bugs, sand get into your shorts
, and the bay water can smell sometimes and I wouldn't trade it for the world.
If you are traveling up to Captiva, just as you pass the Bubble Room your will see a housing complex on the left called Sunset Captiva, wave and say hi