My favorite for years was an old military map, messenger or paratrooper bag. (depends on size you want) Cheap (under $20),does the job well and it will last for years. That works well in rivers as long as you don't run into water above your hips...and the reason I finely caved in and got my Filson Strap Vest. They have a waist pouch too...but for the money I'd rather go with army surplus. You can find the messenger bags at army surplus houses or online.

Examples: http://www.vtarmynavy.com/canvas-map...ulder-bags.htm