I sync most important files between 3-5 devices with Syncthing. Devices are small and portable, 2x laptop, raspberry pi, netbook, I'm going to replace it with external drive connected to my Omnia Turris soon.
I have a few external drives with photos, music, films I liked, everything is evaporating online, torrent trackers are disappearing, content on Netflix is expensive and getting worse and worse, so I 'data-hoard' everything and backup at least twice once per month.
Like a year ago I opened a spredhseet where I log all my bills and it works for me as financial database, ~20 categories of expenses, each has some subcategories.
* Kanban boards
Yellow sticky notes on a fridge.