I take monthly notes with the excellent app Markor, keep my daily diary with the nice app Diary and share lists, notes, todos with family members via Joplin (stores data on my own WebDAV server).

So almost everything is text (with markup/markdown) and can thus easily be synced and merged between devices via rsync, ssh and perl or shell scripts.

Example: when I want to look up notes in either markor's or diary's files, that's easily accomplished with a shell script, e.g.

  cd ~/storage/shared/Documents/markor
  if [[ $# == 0 ]] ; then
     exec zsh
  else
    grep -i "$@" **/*(.) | less
  fi

  python -m http.server $PORT --bind 0.0.0.0

And there's exiftool, ffmpeg, ImageMagick, scripting languages, all in reach, wherever I go.

Markor: https://f-droid.org/packages/net.gsantner.markor

Diary: https://f-droid.org/packages/org.billthefarmer.diary