I'm interested in learning what things you soon figured out were necessary and about the things you thought would be necessary, but learned were not all that important or useful, once you started living aboard.
In a broader sense the question is also interesting in learning what other things you never expected before you moved on board.
Heat. Even in Alabama and Florida heat is nice but farther north it is not optional. If your heat needs a cord to the dock you'll do less winter sailing.
Internet or at least the ability to get email on the go.
Nice to have:
A marina with nice washrooms, laundry, and showers. We are at boat parking lot right now and lack of services suck.
A car. It is great to have a car at the marina but there are work arounds.
Lots of tools. Sewing machine. No room for major projects once boat is in the water and we are living on it. Same with sewing machine. Of course those on larger boats would not have that problem.
TV but sure was nice when we were in an area that had TV.
The hardest is trying to live with one foot on land and one on the boat. It is easier to just live on board and not need or have land clothes and expenses.
I think the ideal situation is to have a house or home on land and a boat at the local dock. Easier to do projects on the boat and yet not have the boat so full of stuff that taking off for a day or two becomes a hassle. We can't afford that yet so on the boat it is.