For utility purposes, I would say this and this.

By using these two pieces of software (MakeMKV and HandBrake) you can make digital copies of any dvd or blu-ray disc you have for free. Personally, I've been assembling a collection of the best movies throughout human history to have when the infection hits and the zombie apocalypse arises. If you're proactive and willing to spend a little more, this is also a great investment for when the lights go out ;)