Well I might as well blast in a few thoughts.
I agree with John with the VHF. I have a full size unit mounted in the cabin and an 8' antenna, the short metal antennas are compact, but not that great for distance the height of the antenna increases the effective range of the radio.
I also have a spare handheld VHF on board in case of an electrical problem.
A decent fishfinder/sonar is a neccesity also, but they have issues which John and SM already discussed.
As for charts and location you must be sure of where you are, and what might be up ahead. I had relied on paper charts and handheld GPS for quite a while, but it can be a pain and very time consuming to accuratley determine your location. Not good if your moving into unknown areas.
Sooooo,, this year I bought a chartplotter and I am absolutley blown away by it.
Now that I know how to use it well, if I had to I could navigate home without looking up from the machine at all. This could be the case if thick fog rolls in.
It displays depths, structures, ledges, rocks buoys and your current position (livetime) on the chart so you can even tell what is coming. The new WAAS technology is sweet and the accuracy of your position is exceptional. I highly recommend one of these units. I gives me a real sense of security out there.
And again I keep my handheld GPS on board in case of electrical problems so i can still call for assistance.
There..... I'm done....
Good Luck