I can't remember them all. A few I've done:
The thrust bearing of the windshield wiper motor armature of my '72 Subaru (below) shredded. I replaced it with a shirt button, and had no further trouble with it.
The threads of the aluminum thermostat housing in that car galled. I drilled clear through out the other side, and installed a smaller diameter bolt with nut on the other side. Installed two aftermarket cruise control systems in the Subaru. The more successful one was supposed to work only with American rear-drive cars with automatic transmission. I made it work on the Japanese fwd with manual, although I had to buy extra magnets to attach to an inner CV joint for the speed pick-up. Same system was later transferred to the Mazda.
Air injection pipes rusted off the exhaust pipe of the '81 Mazda, and also off the 4 air inlet ports in the exhaust manifold. I covered the resulting hole in the exhaust pipe with a screw-type hose clamp, which was barely wide enough to cover the hole. Replaced the threaded connections to the 4 manifold inlet ports with 4 oil drain plugs (which used the same thread size and pitch). It never leaked in several hundred thousand additional miles. A coolant bypass hose rotted on that car. Replaced it with silicone hose from a coffeemaker, which lasted much longer.
When a shift cable for the rear derailleur of a bicycle breaks far from home, the derailleur shifts the chain to the smallest sprocket, which isn't conducive to getting over hills without undue strain. When that has happened, I've jammed it to run on a larger sprocket using a coin, small stone, or other random roadside treasure (i.e., litter).