I use freezer bags that zip up for packing when I travel so it separates everything and packs things tightly. I keep underwear in one and t-shirts in another so it is easy to unpack especially if you are camping or backpacking. I also keep an overnight kit in one for my hand luggage, as it makes sure I don't over pack. They are good to pack sweaters in as it makes them compact and gives you more room in your case.
