I seldom use the dual card slots on my A7iii for the original reason for the 2-slots: backup in case of failure...
However I found that dual slots was handy in one case. Since I never write to Card-2, I never remove it from the camera, which was handy today.
My wife and I visited our daughter and son-in-law for a Christmas Dinner. As we were leaving our house, my wife said, "Please take your camera and tripod because I want a family group Christmas picture."
Well in the midst of packing presents and food for the visit combined with getting the three dogs we were taking ready, I got a little flustered and didn't check if the A7iii had an SD card... It didn't have a card in slot one but, since I never remove the card from slot 2; it was sitting in the camera ready to shoot. my professional pride was saved
I am usually more careful regarding memory. In fact, I have been carrying a memory card wallet with memory cards in the glove box of my car for years. Just in case I forget to bring a card. However, we were driving my wife's car, not mine, for the visit...
It would be easy to beat myself up for the memory lapse but, it ended up as no problem...
Solution 1: Try to do a better job packing
Solution 2: An extra memory card wallet with an SD card in my wife's car