Your chances of seeing a cotton mouth on the trail in the Big Cypress are pretty good. I came two steps from stepping on one that was right on the trail while on a day hike north of alligator alley last month. This was right after crossing a wet portion of the trail. That was one of 3 cotton mouths my group saw that day, so do pay attention to where you step. I didn't see any at the camp sites... but we did see a lot of bear scat both on the trail and at the camps, so I recommend hanging your food. Ticks were an issue too. Besides the one I saw running up my leg, I also found hanging from my underarm the next morning, so bring spray and check yourself. Also, on an overnighter a couple months ago I heard a deep purring/growling sound just feet from my hammock in the middle of the night that I'm convinced was a panther.
Have fun out there!