So, as the simplest backup solution ever, I'd like to get an external hard disk.
One option is to get a case for an existing hard disk and use that. We have a bunch of hard disks lying around apparently.
Alternatively, I could just buy the whole thing. This sounds like the simpler option.
Next, I need to decide what kind of external hard disk to get.
space: >=40 GB
price: as low as possible
I don't have very many requirements. I can get an 40 GB IODATA HDA-iU40 for 7000 yen. That was the very cheapest thing on kakaku.com.