Does the Xbox Series X come with a HDMI cable included in the box or is it something you have to purchase separately?
The Xbox Series X will come with a high speed HDMI cable included in the box. Keep in mind that this is a specific type of cable that is capable of high speed transfer needed for 4k resolution. If you have a long HDMI that you need to use if your console is far from the TV, you will need to make sure it is a high speed cable that can support the max video output that the Xbox can produce.
If you just have a 1080p TV, you are free to continue using the older cable as you do not need the additional bandwidth.