Okay so maybe they won't allow you fit a literal TENT into your suitcase, but you get the idea.
Promising review: "I'm officially sold on packing cubes! These things are amazing! I can't believe I've been packing without them my whole life. These are great quality and come in fun colors. I appreciate the mesh lining that allows you to peek inside. They're also a great value. I packed my clothes, shoes, and toiletry bag for a 10-day trip to Europe as I normally would first, and then packed them in the packing cubes. There was so much more room after packing in the cubes! The items I fit in the cubes and bag were: two jackets, a jean vest, four pairs of pants, two pairs of shorts, a romper, four dresses, a maxi skirt, seven tank tops, four shirts, three camisoles, three pajama sets, 15 pairs of undies, six pairs of socks, and four pairs of shoes. Why are you still reading?? Go buy these cubes!" —Tiffany
Get a set of four plus a laundry bag from Amazon for $24.99 (available in nine colors).