In theory if your boat is properly maintained then you don't need many tools cos not much is going to go wrong.............fkk me was that a flying pig swooping past!
On top of Nos's list I'd be thinking that these other things would be good
Theres only so much you can do on a boat. Spare prop and floating spanner might be good, spare filters and wrench definitely a good thing. I'd use a Boa constrictor type wrench as they don't rust. Most of my breakdowns have been on boats that I've chartered or been hired to drive and for me the biggest area of failure is electrics so I'd be inclined to carry a few spare crimps and a crimp tool.
cheapish tools will do fine for a boat, as I've found that all tools rust if left on a boat and the cheaper ones don't develop the legs that better tools seem too
while your shopping you can buy a kit for your mate KY http://cgi.ebay.co.uk/Womens-Girls-P...item5638c8dc2e