Originally Posted by Emmbeedee
I keep a spare taped to my Montana battery.
At an annual rally last year one of the guys who'd come up to Canada from Vermont didn't have maps for this area in his Montana so I traded my spare card for his empty one and bingo, he had all the maps he needed.
OSM maps, of course... so no copyright violation.
That is a great tip. Thank to all who replied, I will put it all on a card with a backup card.