Regular extras are pencil sketches that I drew in a small sketchbook kept in my purse most of the time. Some are original character designs, some are scenes that didn't fit into the storyline canonically, some belong to various backstories, and some are funny ideas that worked better as a one-panel thing.
Colored extras are inked pieces of various strips (with one exception) that I decided I wanted to color. In most cases, I was coloring the characters to figure out what they should look like for their eventual front view in the characters page. In other cases, I just wanted to color things.
Special extras are random unique things to represent every main character. Felincia's takes place after the end of the story; the rest take place during it. Each one contains at least one original picture, and most of them are silly activities.