I was gonna say, I've never felt the need for any memory card holders. I've got 64GB and 128GB cards for my cameras and never ever fill them in a single shoot. If I have, I've overshot, or done something incredibly wrong.
Dual card slots make this even less likely (but I typically use these for redundancy); but there's one thing about SD cards - they're incredibly resilient, unless you manage to snap them. :D
The safest place, is often in my camera bodies, as they're weather sealed.
Indeed that depends on what kind of photography you're into ;)
With travel, event and sometimes action and wildlife, I'd prefer to take tons of photos and then delete those I don't like instead of missing a great moment and story ;) Also, when I travel, I prefer to have an extra pair of cards, instead of having to search where to buy from. At the most tourist destinations, cards are more expensive and not with the best specs from photo perspective.
With product and portrait photography, it's the other way around, close to what you share. I rarely take more than a hundred images per hour, tops.
Thanks for your input! :)
!PIZZA