Check out the Tenkara Guide sling pack, etc. by ZimmerBuilt (
http://www.zimmerbuilt.com). Among other things, it was designed to be:
1) lightweight
2) easily accessible
3) carries multiple tenkara rods (and western rods) in tubes or out, securely
4) enough room for other stuff (jacket, water, first aid kit, etc) without being bulky
5) bombproof
6) very water resistant
Chris Zimmer did a great job with the sling pack, then he expanded the idea into a whole modular system. The idea is that each individual can decide what fits his or her need. For example, I use the sling pack and small pouch when guiding. When going out for an afternoon on my own, I detatch and carry the small pouch either over my shoulder or on my waist belt.
We've had a lot of days on the water with the modular system now, and we're pretty happy.
Disclaimer: Tenkara Guides LLC gets zero money from the sale of these packs. It really is a genuine recommendation. I like Zimmer's stuff a lot. He uses materials that you can't yet find on "mainstream" gear.