My parents tool around the Bahamas every year in a Little Harbor 39'.
They've got at least three different GPS units; one built into the radar so you can match up coastal features with your charts, one built into the map desk, and at least two hand-held units (ala' Garmin Trek). Make sure the units you're looking at have digital sea charts available, as most of the hand-held units don't (or didn't last I checked) come with sea charts built in. The handhelds also have non-slip, brightly colored (yellow/orange) rubber protectors, bought separately.
You'll want to get into HAM radio, maybe even get a license. Definitely get one for home to try out, even if you buy a different unit for the boat.
Get eneloop batteries and a good charger or two. Also get a solar charger that you can roll out or pack away easily that will charge two AA's fairly quickly.
A wind turbine may be a good idea if you're planning to have a lot of tech gear, and almost certainly if you want a fridge with a freezer. However, most of them are noisy and getting a broken line caught in one while in bad weather will only make things worse. Also, if you have the wind to your back (generally speaking, sailing west) they won't generate as much (as if the boat were stationary) since you're traveling with the wind. If you're traveling east, you'll need more fuel to push it through the air (at a much less efficient rate than just running a more powerful generator off your engine).
An app like Night Sky that will super-impose constellation and astronomy info over a live camera image might be of use. (disc: that's the only app like that I've used and not much - not an endorsement, but it is a cool app)
If you're not already, become a: carpenter, plumber, electrician, mechanic, and eagle-scout level knot tying master. Practice doing separate skills with each limb while balancing on a see-saw.
Get used to making really detailed sailing plans and estimating how long it will take and how much gas and fresh water you'll need to get from point A to point B. Then flush those plans down the toilet. Repeat ad nauseam.
Lastly: have fun, it's great! :)