OK. I'll admit it. I'm one of those who overdoes it and carries a LOT of spare parts. Not only chassis related, but "house related" too. And, believe it or not, it has gotten me out of a bind on several occasions. I also carry a lot of spare hardware of various sizes and configurations - nuts, bolts, screws, washers, threaded rod, assorted fasteners, wire, connectors, glues, tapes, sealants, patches...and here's a handy item to consider...Plastic Tie Wraps of several lengths. I have ties wraps as short as 3" long and as long as 3 feet long. They are very handy to have on hand should something come loose.
Tools? Yep I've got 'em on board, and a LOT of 'em too. Pretty much anything that you can think of, and then some. I even carry a spare Gonkulator!