I asked this when I first came aboard and was given this reference by Sailing Dog to his website
The Cruising Sailorâ€™s Toolkit | Adrift at Sea
This pretty much covers all your needs. As long as you know what to do with it. I.E, no need to buy a full supplies of electrical tools if you do not know how to do the work or plan on doing it. If you want to learn Nigel Calder has a good book on it. Don Casey has a lot of good books on fixing the rest of the boat. "Don Casey's complete illustrated Sailboat Maintenance Manual" is a compendium of a number of his books.
I have been doing a lot of work on my little boat and have 2 small tool bags to cover all my needs. But there is no electrical or mechanical parts onboard.