It depends on the size of the boat and the nature of the voyage. If I was solo on a 26 footer in North America, just coasting, a toolbox and a spares box would suffice. We are on a steel
41 footer planning a circ, however, and a forepeak workshop is nearly essential, given that I almost certainly will have to mill and fabricate pieces as we go and because I have the room as we'll just be three people.
See here for my logic and for the range of alternatives you may consider:
The world encompassed: The three-sided garage
Now, the original owner of my custom boat was thinking ahead and wanted a collision
bulkhead to make a way to have a catastrophic collision
not end in a sinking. The penalty is the loss of a V-berth and a place to stick guests. We determined that guests were going to be rare-ish, and that in the tropics, bedding down on deck
was not a hardship, whereas the absence of a place to do drilling that didn't involve the saloon
table or the deck
in rain would be. Your mileage, tool collection and skill set may vary, but I think I can say even before our own departure that if you can fix things or replace things or carry some less common tools and spares, you will be increasingly popular in the cruising community.
But you'll need an inverter
and/or a Honda
2000 to power the pro grade tools. Very few 12 VDC tools are actually useful.