While I'm confident we'll pass the 21st with no incident (we have until 2036 when Apophis clobbers us on its way back around the sun), my Grand is my doomsday mod. All mechanical so no electronics to fail in an EMP, rebuildable REOmizer on it so I can salvage wick and wire from toasters and boat shops, and I DIY with the ability to do a maceration tobacco extraction, so juice is covered as well.
The battery is the only wildcard. IMR, natch. No PCB to fail. I'd like to mount a solar panel on the door. You can run the wires from the panel through the door and into the magnets from the back, and wire the magnets in the mod to the battery terminals. Might need to shim out the magnets on the door a touch so they stand out enough to make contact.