>>785103
Good question. It hasn't happened yet (on this trip). I've replace the rear tire 6 times, though..

Postie bike tires are just like changing a bicycle tire.
You get the wheel off (advantage of the Postie over newer bikes is this isn't hard--undo 3 nuts), get the tube out, replace the tube with a spare (and repairing the puncture later rather than on the road), wheel back on the bike. I've done it in under 30 minutes.

The magic to avoiding flats is to have reinforced tires, and replacing them when they're half-worn (rather than waiting for as long as possible). I exclusively get reinforced 6-ply tires like the Michelin City Pro/Extra, which last for about 7000 kms before I replace them, whereas 4-ply tires crap out at ~3000 kms.