A sleeping bag is often the bulkiest item in your pack. By compressing your sleeping bag with a Big Agnes Super Light Girdle, you'll make more space available inside your pack. With enough compression, you might even be able to use a smaller (and lighter) pack.
The Big Agnes Compression Girdle fits over any stuff sack, and is a lightweight way to get the compression you're looking for.
Big Agnes part number: ASLG9