Sting Rays Seafood is a must for dinner. Depending on your interests, theres the Tybee Island Marine Science center,
https://goo.gl/maps/5KYGUwFNFYN2 .
The Tybee Lighthouse is a must visit along with Ft. Screven which is right next to the lighthouse. Theres also dolphin sightseeing tours. We used Captain Mikes before and it was a nice tour. Saw plenty of dolphins.
https://goo.gl/maps/GvJh16GKUcm
I used to live in Springfield, Ga about 30 minutes from Savannah. If you have time, be sure to stop on River Street on your way to or from Tybee. Alot of cool shops, bars, and restaurants on River Street along with alot of history.
Enjoy your trip!