Of the most interesting things about SDCC is what you can get at exhibitor booths, we hear a lot about exclusives, this special figure only available here, and things of this nature. Some of the best and most interesting things are not exclusives though but art books and other collectibles of some of our favorite properties.
Abrams Books, especially their Abrams ComicsArts imprint is a source for many of these. Abrams has books of Adventure Time, the works of Jack Kirby, and so many others both of modern times and classic works. One of their newest launching right before SDCC is Steven Universe: Art & Origins showing the development of the series with rare storyboards, character art, and more.