The Hanna Holborn Gray Special Collections Research Center holds a variety of materials, from zines to papyri. Some of them are digitized, for others, you'll need to visit. While it's easy to think of archives as collections of papers, there's a large amount of ephemeral material there as well. For example, the Oreo cookie in the R. R. Donnelley & Sons Company archive. Or the envelope sent to Poetry containing Edna St. Vincent Millay's first poem to be published.