All good ideas, Mr Wizard list is close to what I carry, but my mobile tool kits, so I don't need 4 of them, are also a culmination of the "N-1" theory of what I have needed over the years and didn't have.
The kit has now spilled over into 2 soft sided tool bags that are fairly useful for general road trips with vehicle, snowmachine or dirtbike trips, same bags go into the boat in the summer when out on all but the local lakes where I can easily get a tow and load up and be home, and camper trips.
So adding to the list, trailer bearings. Now just peace of mind. Never used one since the day I needed one and didn't have one and had to drop trailer and drive to a parts store.