J-Man,
There will be times that something new needs to be fixed that may require a tool that you do not have aboard. Such is a boater's life.
So you get the needed tool, fix the problem then ask yourself, "Will I again need this while underway or, is it a dockside project tool? If the answer is yes or maybe, put it in your "boat toolbox."
I have a C30 & keep my toolbox under the chart table on a shelf above the batteries which is not a big area for tool storage. Along with this, I have a cheapo 70 piece socket wrench set. Twenty years ago, I bought two "Metrinch" socket sets. A fitting spans both US & Metric sizes hence, only half the fittings required.
The advantages are that they will loosen bolts when the normal hex-points are stripped. It does not rely on the points of the bolt head but rather, it tightens down on the flat sides. I keep one set on the boat & one at home. I don't know if they even make them anymore. A very well made tool both by design & material. I keep them shiny like jewelry.
CR