I am sure some of you might be aware of the Rite in the Rain Company, but I recently used some on the water and it really impressed me.
So I have used their notebook writing products for quite a few years on the job.
Recently I got ahold of some of their Weatherjet Ink-Jet paper and made some stuff for on the river and it worked great. I made some river maps and then duct taped it to my raft and made some notes on the water.
Basically you can print out just about anything and not worry about keeping it dry.
It isn't really cheap at a little less than $1 a sheet, but way better than a soggy map.
Here is the link to their site, Weatherjet Ink-Jet paper