GPS & Computer
I''ll second the sentiment on the Panasonic Toughbook. Got mine on a closeout a few years ago. The only caveat is that they have some sort of draw against their battery even when turned off. Have to recharge mine about every other week.
Also, I was able to get a 12V adapter for mine, so I don''t need to run an inverter to power the unit off boat power. A side benefit is being able to run mapping software in my car on road trips.
Another advantage over a chart plotter is having an honest to gosh Intel based PC that you can run software on. Handy for email and such...