For me the elephant in the room, well in the hallway, is my new bike's SRAM Apex indexed shifters.  Great big mysterious modern things sitting on my handlebars.  I can just about set up the indexing if it goes off, but I have no idea what I'd need to do to replace the brake or gear cables (well, I do know - I'd download the SRAM manual and go on youtube).  I ought to really, to be prepared for roadside emergencies.
 
I can do most other things - provided they don't have anything to do with spokes.  Wheel trueing is beyond me.
 
I do lift the bonnet of my car.  I'm a dab hand at filling up the windscreen washer resevoir.  I even mix my own screenwash sometimes (really hard core car maintenance)