Paul (rumbleseat) once posted a list - It might be over on the tech tips site (billB). I think his list is likely similar to the one posted here. My philosophy... I carry (usually) a small collection of tools - they all fit in a small bread pan. Almost nothing for parts - I figure that whatever I need, will be what I didn't bring. I get the wife to bring a cell phone & AAA card. Haven't needed those, either. I usta try & carry a bunch of spares, but as posted, not much room for all the junk - so I leave the stuff at home. So far, so good. More than 10 years, and not on the hook, yet. One rule I set for myself, long ago... Things that are readily obtained at any parts store, I don't bring (oil, coolant, hoses, plugs). Other things, that are big, heavy (carb, gen, starter, axles), I don't even consider bringing. Sometimes I'll carry really small items, that are a 'pain' if you need them - a gen brush spring, set of points (one side only - it will run on one side), condenser, fuel pump diaphram. (Haven't needed these items, either.)
I used to carry water - thinking about overheating flatheads. I don't carry that, anymore, and we carry a case of drinking water bottles.
I don't even carry a jack - probably foolish, but there always seems to be someone around with one, even if it's AAA. Haven't yet needed one.
My range of travel is generally no more than 500 miles from home - so this influences what I do/don't carry.