Save your receipt for free parking later or at another beach
The guys at the gate will tell you to save your receipt if you decide to come back later in the day. You can gain free access the same day. What they won't tell you is that you can actually re-use your receipt at any Collier County beach that same day (they all look the same and don't indicate which beach they came from). So, feel free to visit Clam Pass Beach in the morning, and re-use your receipt and visit Barefoot Beach or Vanderbilt Beach in the afternoon (or vice-versa)!