Let's go through the contents of my chest bag.
Head phones, I carry my blackberry to answer calls and also it takes all my pictures. I have an 8 gig card that is full of music. I am always jammin when fishing. Small line clip. Foam handled pliers. Finger strippers to cover my line holding finger. Hook sharpener. 30 pound fluorocarbon. Extra leader. I use only furled leaders now. They throw big flies much better. On the opposite side of the leader I also have a few hooks for my tube poppers.
Boga grip. This goes in the back outside pocket. I have the carabeaner to attach it to the loop on the side pocket. I bent over once and it fell out. Luckily I was in shallow water.
Of course flies. I carry flies in the same little bags I sell them in. This keeps them flat and nice to fish. They lay very flat and I can carry about 40 in my pouch. Now obviously I never take more than 6-7, but the point is space. There are no boxes big enough to carry my flies and still fit in my pack. Boxes also limit the amount of flies I can carry and just add weight and bulk.
Cigars are a given as well, but that is a whole other post.