While not widely advertised, the Deer Island Coastal Preserve has verified that camping is allowed, at no charge.
When the pandemic hit, I hit the road. Drove south to Biloxi, parked, hopped in my kayak, and paddled to Deer Island. It’s less than a half-mile off the coast, but far enough away to be left alone. Great paddling, quiet camping, lots of birds. Downsides included: casino views on one side, and a lot of litter along the shores.
I’ve been told it gets crowded with parties and boats on weekends, but I didn’t see any of that. Just the trash left behind.