Riptide makes a very good point--
Try and pick up an 8 or 9 weight outfit ---- even a super cheap one. You'll have a much better chance of tangling with something, and there should be plenty down there to chase including striped bass, sea trout/weakfish, bluefish, puppy drum, fluke (summer flounder), spanish macs etc as well as any kingfish/spot you might run into.
In addition to handling the fish you hook into, it will be much easier to throw SW flies size 2-2/0, deal with the wind, and most 8 weights and up gear (both rods and reels) are built to withstand SW corrosion.
A good spritz and rinse with fresh water after a day fishing in SW should be standard medicine for any fishing gear, including 8 or heavier weight gear, but be super sure you do this with your 4 weight outfit because it may not have corrosion proof guides and reel seat on the rod or anodization on the reel.
A handful of some simple flies like clousers and deceivers and you're good to go.