A compression sack is a nice way to compress a bunch of clothes or a sleeping bag to a compact size. If you don't mind wrinkles you can compress your clothes into one and save room in your carry-on travel case for other items. Or you can use one to hold your dirty laundry. I like to use a compression bag for my kids' sleeping bags, because they are much stronger and more compact than the carrying bags that come with sleeping bags.
Outdoor Research makes Ultralight Compression Sacks in a variety of sizes.
