Tool requirements are hard to judge. What you need depends on your mechanical ability and willingness to work on the engines and other systems. Some people are happy with a single tool (checkbook or Amex/Visa/etc. card) and others have essentially a full machine shop.
As far as essential spares go, I always have the following:
1) fuel filters (at least one on engine filter and two racor filters)
2) spare belt (s)
3) oil filter and enough oil for a complete change
4) Enough transmission fluid for a change
5) Air filter (although this isn't as important as the other spares because you can run without a filter)
6) Impeller
7) a couple of hundred feet of electrical wire in various gauges along with matching connectors
8) Spare bilge pumps and float switches (my boat is a woody)
9) Varnish
10) paint in all colors used on board
11) small tube of 3M 4000
12) 2'x4' piece of 8mm marine plywood (my boat is a woody)
13) 1 box each of #12, #10, #8 and #6 screws in stainless and bronze as appropriate. Screw types vary from pan head to wood. I also keep a selection of machine screws
14) a variety of cable ties and clamps
15) a couple of dozen spare hose clamps in all appropriate sizes
16) 10' of 3/4" hose and a few feet of 1.5"
I also keep a spare set of copper gaskets for the high pressure fuel lines and a spare injector.
My basic on board tool kit includes:
1) 1/2", 3/8" and 1/4" drive socket sets in both standard and metric
2) All needed combination wrenches
3) several vice grips
4) three sizes of slotted and phillips screw drivers.
5) complete set of allen wrenches
6) 3/8" and 1/2" drive torque wrenches
7) DVM with clamp on ammeter
8) wire strippers and crimpers
9) rechargeable tools (drill, driver, saw)
That covers the basics for me, but I like to be able to repair most things.
oops forgot a few things - wood chisels (3), hammer, caulking iron, mallet, calking cotton, seam compound, dolfinite, japanese pull saw, bevel gauge, level, chalk line and about 10 clamps in various sizes.
