Back up everything with this discounted 16TB external HDD from WD
All the storage space you'll ever need, surely?
Right now, a pair of massive 16TB external hard drives are going 'cheap' on Amazon UK. Despite RRPs of over £400, you can get a basic model for £245 or a slightly fancier box for £270. Either way, you'll have a ton of storage space for backups, video projects, game install directories and other media.
My colleagues at Digital Foundry pick these drives up regularly for their video production work, as capturing game footage and creating YouTube videos quickly causes standard hard drive sizes to fill up. You never want to be in a situation where you're forced to delete your old work to save the new stuff, so having a capacious backup like this is perfect.
Get the WD Elements 16TB external HDD for £245 (was £407)
Get the WD My Book 16TB external HDD for £270 (was £424)
WD is generally regarded as the leader in this space, although their chief competitor Seagate is sometimes preferred. (For the sake of comparison, Seagate's 16TB expansion drive is selling for £289, but it's out of stock.) I've personally been using WD drives since the mid-2000s (gosh, I feel old) and haven't ever experienced a drive dying on me, which is somewhat miraculous.
It's also possible to 'shuck' these drives, ie remove their outer shell to get the 'white label' drives inside and stick them directly into your desktop computer. Obviously you lose out on portabiity, but access times are reduced somewhat, which helps when you're viewing or copying over files.
In any case, if you need 16TB of expansion, you probably don't need me talking your ear off about it. These are solid drives, this is a good price, end of.