The Super Days Worth was designed to be the only fly box you need for a day of fishing.  It's triple layer design allows you to hold a ton of different sized flies.  The magnetic side is perfect for small nymphs and emergers, while the leaf page has slit blue foam to grip your big nymphs and streamers.  The top side is designed to hold your dry flies and keep them from getting smashed.  All of this and the Super Days Worth fits right in your pocket.