Most things i would buy online when i lived there. The Academy stores do put out quite a bit of stuff during the season and as it approaches. You have a Gander Mountain north of town by the airport, and another down in St. Augustine by the outlet mall. There is Bass Pro in Orlando and in Savannah. Dick's Sporting goods in the Orange park mall and in the St. john's town center both started carrying waterfowl gear last season.
Academy seems to have the better prices. Gander down in St. Aug will randomly, without ad placement, run decoys on sale. Shotgun shells are tough to come by. Don't know why Gander thinks we needed "T", "BB" and "BBB" shot there, but that is what they seemed to stock the most of. Go early for shells and stock up on them, because once the season hits the good shot sizes get scarce.
Watch Craigslist...found plenty of deals on decoys while i was there as well. If you are into deer hunting, venture up to Georgia. If you are military, some of the places in St. Mary's will sell you a state license for the resident price...that is how i got mine. If you want to have some fun, get into hog hunting. I killed 3 last spring there on a private hunt club.
Really miss duck hunting down there, but i get my time in when i come down for leave. Good luck to you.