I hate it when members join a thread late, then ask questions that were previously answered - but forgive me if I repeat previously offered suggestions. Some of my repetition will be in support of very good recommendations.
Now, I have not been to the Keys in a few years, but I used to do dive trips there - and my first stop after checking in was the Key Largo K-mart. There is also a huge dive store in KL and much more in case you need more than you take. Of if you are staying further down the road, there are many more stores.
I guess you both have DAN dive insurance and have already shopped for decongestants? Hate to see a newbie ruin their first dive trip unable to equalize. Get the good stuff that requires ID and signature from behind the counter.
The portable luggage scale is a very good point. We travel with one as well and has readily proved it's worth.
Essential! And the first things you weigh are your bags. I have a couple of pricey pieces of scuba luggage I never use any more because they each weight 5# or so more than some of my lighter bags that I do use - allowing me more leeway on packing. The airlines are killing us on weight limits.
We are traveling to a fancy resort for a friend's big birthday bash in the Keys.
As suggested, pay for the extra bags and take what you want - up to 2 - 50# checked bags each, 1 roll-on each, and 1 backpack each. My last flight on A.Eagle a couple of weeks ago, some guy had a huge, rolling suitcase - well beyond legal limits, and he got it on easily, but I do stick to the dimensions listed. (He was an odd looking fellow to be traveling to Lubbock, hippy looking with clothes that looked like they were falling apart, but I glanced some interesting looking middle-eastern clothes or rugs he messed with in his bag.
Maybe they gave him a pass because it was easier than finding a translator or dealing him? Surely he didn't fly in from overseas with that as a roll-on? Who knows.)
Problem solved!
I wish more airlines would do the "gate check" thing. Air Canada does it on some of the short hauls - allows you to really pack that "carry-on", but never have to take it into the cabin.
Bill
It's common to see that on CRJs and other planes with smaller cabins. Airlines reconfigured overhead bins of larger planes to better accommodate roll-ons after they became so popular, but CRJs and the like hardly have room for the personal bags. Small overhead bins on one side only, and even less room under seats.
Caution: I've seen cameras broken in roll-ons when they were gate checked, and I've seen people grab the wrong one. Tie some colored ribbons on all handles of yours, but cameras, other breakables, medicines, and most important stuff go in your backpack!
Shipping some of your luggage ahead of your trip may be an easier and cheaper option.
Have you done that? Pricey, and how do you know it'll be safe & available when you arrive?
Also remember to dry your gear as well as you can for the flight home. The water can add some pounds and in humid climates this can be hard to do so if you can hang your gear in an air conditioned room to dry. Also if you brought lights with you throw away any batteries to save a few pounds for the ride home.