I am a minimalist and fight continually against the drag of Orvis and the fly fishing gods to keep my kit small. I have for the last decade used a small Filson waist pack (http://www.filson.com/fishing-waist-pack.html). Wonderful quality and the right size but I go tired of trying to get it over the waders, under the fleece and around the rain coat. Last year I switched to an Orvis shoulder pack. I got the smallest one (I got it on sale so I might be discontinued). Right size and well made. The problem I have had is that it slipped off my shoulder every minute or so. I have used contact cement to attach a piece of a yoga map to the strap and that seems help. I am still holding final judgment.
David