On our way to a remote cabin, when the alternator failed. Well, the alternator itself didn't fail: the bolt holding the distribution lead on corroded through and fell off. No cell service, long ways to any help, and my then-new girlfriend was not at all happy. I wandered up the road and found a piece of wood I could whittle to the right shape, and then dug through the boot. I hung the wire onto the bare stub of bolt remaining, locked the scrap of stick over it, then tied that on with the strap from a pair of old swim goggles. We made it the thirty miles to the cabin, had a good weekend, and the fix was solid enough to make it a hundred miles back home. Oh, and the new girlfriend is now my wife, so all things considered that's by far my most successful hack.