What preparations are necessary is different for everyone. What to pack? What not to pack (maybe as important!)? What to plan ahead, and what to sort out as you are on the hike? And so on. One thing that most people need is their phone, and while basically everyone will remember to bring it, there are a number of things you ought to do with it before leaving, as well as other tech stuff that you probably should look into.

For any type of trip

• Make sure relevant documents are available offline in your phone (or computer if you are bringing one)
  There are many instances where your hiking will bring you to areas with poor or no connectivity. If there are documents and data that you need while hiking, such as maps, gpx-files, hotel booking confirmations, spreadsheets, or whatever, make sure that they are available offline.
• Clean your phone from saved data such as photos
  It is a pain in the butt to run out of space on your phone while out hiking just because you want to take zillion photos and videos of that cool waterfall. Make room on your phone before you leave!
• Make sure your charging cables and equipment are working properly
  It sucks to start hiking and then realise that your charger doesn’t work.
• Check what kind of adapter you need for your charging equipment
  This might seem like a no-brainer, but I’ve met a lot of people that didn’t bring the right kind of adapter, and had to panic-buy expensive ones at the airport.
• Turn off background location access for a lot of apps that do not need it while you are away, for instance Google Home.

If I go to a country with no roaming partnership with my telecom provider:

This is a rather specific list, especially if you are used to travelling within the EU where all/most countries allow you to use your normal home rates when calling and surfing. But if you are a non-EU member, or are travelling to a country beyond the EU borders, check carefully what your telecom service provider will charge you for just getting an SMS and so on when you are in Japan. It can get expensive pretty fast.

• Turn off data roaming on your phone.
  Doing this prevents most of the extra expenses that can occur. But sometimes you need to check your email, or search for something even if you have no native connection and no WiFi.
• Turn off automatic photo back-up
  If you are like me and snap away a hideous amount of photos, you don’t want to pay money for backing them up!
• Turn off automatic app updates
  Make sure everything is up to date before you go, and make periodic checks when you find WiFi. Working in information security may have made me paranoid, but it is a good thing to always try to have the latest version of all apps.
• Turn off auto download of MMS
  Datawise, this might be basically nothing, but a lot of telecoms charge per MMS, and SMS, and sometimes that is a *lot* of money each. Especially if those MMSs are ads or some other crap you have no intention of ever caring about.
• Uninstall unneeded apps on the phone (for instance apps for your local commuting).
  In essence, go through your phone and check each app whether you have any need for it while on the hike. If not, delete it. You can always reinstall it when you come back home.
• Buy a local eSIM and install it on your phone
  Some local eSIMs might have unlimited data, but most do not. Make sure you keep track of how much data that you have used. An eSIM company may be really cheap if you keep within the allowed quota, but can turn hideously expensive if you use more than that.