For a long time I was looking for a comfortable backup routine that works for my use case of having multiple devices (2 linux laptops, 1 windows desktop, 1 phone) and includes off-site cold storage. Cold, as in, disconnected from the internet and therefore unhackable, and off-site for protection against a burglary or fire. The solution I settled for is simple and cheap:
Instead of hauling around expensive/big/fragile external harddrives, I bought two 256GB USB pen drives, encrypted them and copied over my most important files.
I've met people who read (non-fiction) books and they just remember all important details effortlessly. I'm totally not one of them. The concepts might have an impact on me for a while but then quickly fade. A year later, it would be challenging in a discussion to refer to what I've read with any confidence.
Thankfully there are options to help with that. My system consists of taking notes and then boiling them down into what fits on a flashcard so I can continuously revisit it as time passes: