The ideal solution for maps is laminating them with acetate sheets. While managing without bubbles is somewhat of an acquired skill, it doesn't require a machine. They'll be nearly indestructible at the cost of being somewhat more difficult to fold. Best of all you can write on them easily with a permanent marker and wipe it off later with alcohol. (Fine point Sharpies and prepackaged sterile wipes work well.)
[ On a side note you ought to be using permanent inks or pencil regardless, because water based inks don't fare well after a swim. ]
Short notes you can put on the back or side of the map. Long form writing like a journal is best done out of the rain. If you need to do it regularly in the rain I'd get used to carrying a poncho or light tarp and a couple of bungie cords to allow instant shelter. Important information, like research notes, should be taken down on separate papers and transferred into the journal or notebook later in the safety of a reliable shelter like a tent or cabin. Don't be the guy who drops a notebook out of three waterproof bags into a puddle.
As far as protecting regular paper goes I'm fond of sandwich and freezer bags. Clear sandwich bags make a pretty decent "field expedient lamination device" for any information handed to you on small card stock that you may need to read in the rain. Freezer bags work well for notebooks. Both are a lot cheaper than specialty pouches and the fact that you discard them after saves wear and tear. Wrap the bag containing your book with a shirt or towel for extra protection and keep it inside the waterproof bag in your pack.
If you just want a memo pad that can be kept out of your pack the waterproof paper ones aren't awful. They do work and give you some protection against being submerged, but they're much less pleasant to write on than paper. Short of being required to take notes at a sprinkler research facility I'd opt for a hard-shelled waterproof case and regular pad. The biggest advantage of the waterproof pads is being flexible enough to be comfortable in a pocket.