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Dad Photographer
Why would you consider taking two digital bodies (M8 + M9, for instance), but no way to backup your pictures ? How often did one of your Leicas break during your travels ?
During our recent Alaska trip, my wife lost several hundred photos via a defect and unrecoverable memory card. Trust me, you don't want to go through this (both of us took photos, I had the only keepers); backup your photos, either via a drive ("digital wallet" - they are much smaller than one of your Leicas), a tablet or a laptop, on a daily basis.
It happens. Statistically more frequently that film x-ray damage, or, I'm sure, more probable than your M9 breaking.
Roland.
I would not take only digital cameras. The M 4/3 would be an add-on to the other cameras, if I wanted a back-up digital camera. I always have the Ipad with me too. I may take along a small sized external drive too.