[Ron Reefman]

If the weather is good you can easily kayak out to Little Bahia Honda Key from shore (maybe 1/4 mile).

From the boat ramp at the end of the SW end of the Seven Mile Bridge you can easily get to Little Money Key (Florida Bay side of the bridge and 1/4 mile)
Or to Money Key on the ocean side of the bridge and is much better snorkeling (1 mile from the boat ramp)

If you are really adventurous, Molasses Key is on the ocean side of the bridge (about 2 miles from the boat ramp). And I'm still working on getting my wife to let me take her there in an 11' Zodiac with a 20hp outboard!

Pigeon Key is 2 miles out from the NE end of the bridge, where the Railroad Museum is. We haven't been snorkeling there yet, but we walked out the old bridge and looked down from above and I can tell you I want to go. Again, my wife isn't a fan of small boats, open water or outboard motors!

Bahia Honda probably does as good a deal as anybody with their charter boat out to Looe Key and the big reef. It's a really big area and the bottom is row after row of long ridges (hills) so water depth varies from near zero in some spots at low tide to about 15'-20' in the valleys at high tide.

"We will be staying in a camper and there has already been talk about setting up a temporary aquarium on the kitchen table or in the bathtub (shh, don't tell my brother-in-law)."
We take a big cooler and set it up in our motel room with a 120 volt bubbler to keep live stock. And I do a 50% water change every morning and every evening. I even take a small heater because at 72 degrees the room temp air going through the bubbler cools the water down pretty quickly.

Are you camping at Bahia Honda or some place else?