Re: What tools do you keep on board / What have you fixed on the water?
I keep a good sized tool kit on board all my boats. Pliars, sockets/drive, vice grips, wrenches, screwdrivers, hammer, etc, all the usual stuff. I also keep jumper cables, a large diameter tow rope (never tow a boat with anchor line!), duct tape, electrical tape, and some other tools including a filter wrench that fits my fuel filter / water seperator. I also care a grease gun.
Also, have several lanyards for your tools so that any tool that's used where it might get dropped overboard can quickly be attached to a lanyard to avoid losing it.
I have never had to make anything more than minor "tighten a screw" repairs, but I have helped others who were dead in the water several times. On was a group of younger boaters who ran the battery dead while playing the stereo on a sand bar, another guy had the adj bolt of his alternator come lose, towed a guy with a dead engine, etc.
A couple of important points:
Make sure you know how to change your prop--and by that I mean take it all the way off and put it back on--in your driveway or in some other safe place. That way you KNOW how to do it when the time comes. And if you boat long enough, it WILL come.
Keep in mind, if you boat big water and have a sterndrive, you may have to get in the water to change the prop. That is when you'll thank yourself for knowing how to do it in advance.
When you do this dry run, you'll discover interesting things. For example, I discovered that my adjustable wrench that I thought would fit the prop nut, did NOT, in fact, fit the prop nut. Discovering that in the driveway saves a lot of time and expense!
Also, do you have a lug wrench that fits your trailer lugs? I got caught on this once. No, your car/truck probably does not have one of those old school crossbones wrenches, it probably just includes a wrench that fits the vehicle's lugs. What are the chances your trailer's are the same size? About zero.
For spares, I carry a spare prop and all prop hardware. Nut, retainer, etc. I carry a spare fuel filter/water seperator, 2 qts of oil, WD40, electrical wire, fuses, 2 flashlights, spare trailer bearings and misc hardware.
Grouse