Inevitably through the use of nets and being moved into and out of the plastic keeps, collected fish often get damage to their slime coats. External lacerations, especially on the eyes, create an opportunity for infection. For collected fish, I like to use 10 mg/L nitrofurazone in the water for the first 24 hours that I have them. This antibiotic is moderately effective at a broad spectrum of external bacteria. I treat in a 5 gallon bucket or 30 gallon Tupperware. Nitrofurazone also has the anecdotal effect of breaking the life cycle of cryptocaryon somehow and I see this as a potential added benefit as a few cysts are common in batches of wild fish. I have the fish and inverts I collect in 30 gallon Tupperware (filled with about 20 gallons) and powered by air pumps with airstones bubbling for a few days with no problems. I stay on a saltwater canal and can do 75% water changes daily if necessary. Something to consider is potential temperature where you will be storing these fish. Keeping fish collected midsummer in an air conditioned house may cold shock the fish. On the other hand, keeping collected animals on a sun on a deck will likely be too hot. I keep what I collect outside in the shade and have not had problems in summer months. If you are going to collect gorgonians I recommend waiting until the last possible moment. I usually go collect them from the Bahia Honda bridge (marked in the maps section) the morning that I leave. It is important if you are going to keep small fish, like neon gobies, for a few days before heading home that you feed them. Using green dip nets to scoop up sargassum and dunk all other little shrimp into a five gallon bucket is usually how I keep all of the sizes of fish fed. To bring fish home I have a charge inverter which plugs into the cigarette lighter of my car, changes the DC from the battery to AC, and allows me to plug in the same airpumps I was using to bubble the Tupperware. Here is a cheaper one from Walmart which works fine.
Battery powered air bubblers which work on D batteries also last at least 5 hours in my experience and I set those up for redundancy. Another strategy for transporting is renting a small oxygen tank from a welding store and bagging everything up. This seems like a cleaner option but starts to take up serious space and bags if you are moving large gorgonians for example. If you are going to travel via airplane to the keys and want to bag up fish and UPS overnight fish home to yourself, you could bring these oxygen receptacles with you on the plane to the keys .
I like to use a chemical which binds ammonia/nitrite (amquel/prime) to help keep my mind at ease during transport.