Buy it on: Amazon
While we've focused on the traditional external HDDs, it's worth noting that external solid state drives are also compatible with the Xbox One X for those who prefer to stay on the cutting edge.
The cost goes up significantly for less storage space, so what's the upside of an SSD over an HDD? Most notably is that these solid state drives are totally silent, adding absolutely no extra sound to your gaming area.
They also offer much faster transfer speeds, but that's less relevant since you probably won't be frequently transferring data to and from different devices when using the drive as an Xbox storage location.
While this 1TB option will set you back a pretty penny, the 512GB versions lower the price substantially, although obviously at the cost of reduced storage space.