Figure out what kind of toolbox that you prefer. Some use fishing tackle boxes which are great if you haul a lot of small parts to toolboxes with slide-out drawers.
What tools to take along is also up to what you need. When working on your boat, have your toolbox handy and whatever you needed to work on it should go in there. Always carry spare parts, especially the ones that may have a habit of going bad like spare servos. Whatever you leave at home is generally the part that you're going to need lakeside, at least that's what happens to me!