I like to carry a small notebook to jot down reminders, directions, and thoughts while I hike and backpack. I was carrying a Rite in the Rain notebook for a while, but I didn't actually have a problem keeping it in a plastic bag with other stuff. I wasn't trying to write a haiku during a thunderstorm. I also ended every trip with tons of spare pages, having only used maybe 20.
The Moleskine Volant Mini is tiny. I don't own a scale, but I doubt it gets much lighter. It fits in my wallet. The pages tear out, and as a bonus, the grey ones match your Palomino Blackwing 602's.