There is no storage other than the SD card. The store had the 128 GB card on sale for only $10 more than the 64 GB card, so that's what I bought. I've been using a 64 GB card in the G7X II and haven't come close to filling it up on recent trips. I normally reformat the card in the camera after I transfer pictures to the computer. On a 12-day trip this summer, I took 900+ Raw pictures and one short video, and didn't come close to filling up the card. I haven't erased those pictures from the 64 GB card, and the camera says I can still shoot another 1100 Raw shots or 82 minutes of video in the remaining space.
All that said, perhaps one should not put all the eggs in one basket. So a lot of folks would rather carry several smaller cards than one 64 or 128 GB SD card.
Also, some older cards may not work in the camera. On an extensive trip right after I got the G7X II, I also took my S120 along, in case there was a problem with the new camera or I might want to take the slightly smaller S120 out some days. (I still didn't know whether I preferred the new camera in all circumstances.) It turns out that I never used it. When I filled up the memory card in the G7X II, I decided to take the 32GB card out of the S120. It was older, but rated a 10 in speed and works fine in the S120. The G7X II wouldn't recognize it at all and wouldn't format it, so I put it back in the S120 and got the spare 4 GB card out to use, and then bought another card (the 64 GB that I've been using since) when I got to a town.