I use a "fanny pack" almost all of the time. I have a couple of sizes, but the most use is a smaller one with a water bottle I bought cheap from Sports Authority. That and the pockets in my shirt give me all the storage I need. The only problem with "fanny packs" is dunking them when you are wading in deeper water. Seems to me sling packs would not help you back, but I've never used one.

Another option would be a light back/chest pack combination like the Orvis Tri Pack or Wm. Joseph Exodus Pack. This would help balance the load front to back and give you plenty of storage.