As a current mobile tech who just cleaned his van out wow I got a lot of stuff. All depends on your skill set and how deep are you going to get into it to fix it in all honesty. Electrical meters, amp clamps I’m partial to Fluke for all of my meters, rethreader kit, induction heater, good wire crimp set with strippers and terminal ends, vice grips, Hose pliers, hose pick, mini pic set, chisel and punch set with a hammer and dead blow hammer, socket set, a quality bit driver set, brass punch, files, as well as a socket 1/4 to 1/2” sizes up to 1” and 27mm or so and wrench set. Ratchet wrenches could be on the list to, mini ingnition wrench set, long reach pliers, telescope magnet, mini telescoping mirror, caliper guage, breaker bar, pipe for breaker bar, certainly ratchets, drill bits, left handed jobber bits, drill, extensions for sockets, I have my power probe 3 kit if you get into dc electrical,
I can think of a lot more and some was mentioned like pullers and souch. In The end it all depends on skill set and how deep are you going to get into it. Look all over the boat see if you can fix it and make a list of tools you think you need. I just kept collecting as needed for over 20 years so what I might bring could take over its own room and be my workshop.