Position a milk crate on the floor or another flat surface. Place the bottom of the crate against a wall with its open side facing you.
Arrange books and other media in the milk crate's cavity.
Place another milk crate next to the first crate. Thread a zip tie or wire through the crate's holes to connect the units, if desired. Fill the crate with books or other media. Continue this process until you run out of room for additional units stretching horizontally.
Stack a milk crate on top of a filled milk crate with its cavity facing you. Attach the top crate to the bottom crate with wire or a zip tie for stability. Fill the milk crate with books or other media.
Continue adding units horizontally, then vertically, until you run out of space for more milk crates or have stored all books and other media.