Spent a week on Marco Island in December.
Activities
Take a cruise to 10,000 Islands area. We used Capt Ron's. You will see all aquatic and feathered wildlife
Swamp Buggy and airboat tours in Everglades
Go to Tigertail Beach. You park then have to hike and wade to very private and pristine white sand beach
Naples Botanical Gardens - wife is a Master Gardener and even I enjoyed this place
Food
We stayed in a condo and fixed most of our meals. However, I strongly recommend:
Joey's Pizza and Pasta
Capri Fish House - go in the evening and watch the sun set. Sort of a dive bar look but great food.
Pelican Bend - next door to Capri, more of a family dining feel, but great seafood