You might try looking in an office supply store for the heavy plastic zip pouches used in a day planner. They come in 8 1/2 by 11 inch size and are made of heavy plastic probably in the 10 mil range with a zip lock top that would make it easy to get at your materials. They are usually sold individually and you could put them in a large notebook to make organization simple.
I know the one I use in my day planner has lasted for several years even though it's over filled with all sorts of "stuff".
Just a thought...

Jim Smith