During the course of our trip to Europe we used a pretty simple list of gear:

Cellphones: I had my Samsung S11+ and my kids each had their relatively newer Apple iPhones.  The my phone is on A&T and it worked well for the month I was away with the Passport service. Voice, texting, and data were all very usable throughout Europe. The kids are on T-Mobile and their phones worked pretty well for texting and phone calls, but the slow 3G data that is free for all T-Mobile customers was not super useful.  In the end, most of the places we stayed at had WIFI (including several trains), and that was the main way we connected to the Internet.

Computer: I brought my Acer Chromebook Spin 13, and I was glad I had it.  The most significant help was related to actually making online reservations.  Once reservations were made using the Chrome browser, using the corresponding Android app (for airline, hotel, car rental, etc.) was sufficient.  I also used it for note-taking at the GTD Summit.

Tablet/eReader: I did bring my Kindle with me and that was very useful for reading.  I decided to not bring my iPad and that turned out to not be a problem. 

Camera:  I used my Sony VII and my phone. Conrad did bring his XLR, which turned out to really expand the breadth of photos taken.