Boîte-en-Valise or "Box in a Valise" is an object created by Marcel Duchamp which is now in the collection of the Philadelphia Museum of Art. See its current cataloging in the Museum's online collection here. It's a museum in a briefcase, a fold-out ensemble of reproductions of works of art. I've always felt it's an excellent example of Duchamp's sense of humor about art and collecting.

I am an employee at the Penn Museum, full disclosure!
GLAM / Philadelphia Museum of Art project contributor