What are some of your favorite supplements?

On rare occasions, the scope of a film can get to be so enormous that the film itself can't capture everything. Sometimes you'll have supplements that provide the other half of the story, and it completely recontextualizes the film. Specifically, I'm thinking of Close Up Long-Shot. To see the incredibly sad aftermath of Close Up, where Sabzian completely failed to live his dreams just fascinates me to no end, and none of this was in the original film itself.

And of course, not all supplements need to be so grandiose. It's also fun to see a directors early works that weren't quite big enough for a standalone release.

What are some of your favorites?