Practical and useful
Think about your international driving license
Internet (Wireless - mobile data 4G, 5G) - GPS
In hotels and motels, wifi is very often present and of good quality for current consultations or even video.
In public spaces, they are often of the correct quality, but the downside is that you often have to connect to different networks.
4G-5G mobile data (roaming)
Depending on your subscription, see if the country is included in the package (Europe is automatically included "voice and sms", check the amount of GB in your package for Europe.) Or often optional for international. Contact your suppliers for more details.
Consider having a VPN for security to protect your data. Prefer paid (~ 10 € / month) to free, often inefficient or dangerous.
Remember to switch off your "Mobile data" on your mobile phone before turning it off, because if not when the mobile is switched on, it will activate and this can be expensive up to 10 € / Mo (~ 1 email without attachment ).
If you need a GPS, Google maps comes in handy because you can use it offline. In the menu, select "Offline plan" then "select your plan" adjust the area to download then "download" in this mode, you do not have access to real-time traffic