A:Answer BestBuy has 1, 2 & 4 TB external hard drives on sale right now at VERY good prices! While I think there is space to install an internal hard drive (or expand the SSD), the easiest thing for me was to buy an external hard drive.
Other goodies you might consider:
You can also pick up a DVD/CD player for less than $25. that plugs into a USB. The RAM memory is expandable up to 32GB for a good price, and that's easy to install (or you can pay the GEEK squad).