The "Black n Red" notebooks you can find at grocery stores are actually really good, unless they've gone downhill in the last couple years.
I like Clairefontaine notebooks quite a bit.
This notebook will hold up well as a back pocket notebook and the paper quality is excellent, just don't let it get soaked of course. All of their notebooks are good quality but I like their spiral bound medium notebooks because I want my paper to lie flat when I write on it.
Rite in the Rain notebooks are okay but the pens I like don't work on them, and you can forget erasing anything if you're using a pencil. Still, when the application calls for water resistance you can't beat them. I have a field notebook I've used while sitting in the open in a pouring rainstorm day after day and I never lost any data, the paper just gets a little wrinkly when it dries. That notebook has probably seen at least 100 soakings and it's still going strong.
I also have piles of those $1 composition notebooks. They're not ideal but they're tough and cheap and comfortable for writing on my lap or in the car, and I can use my dry fountain pens without too many issues.
Very recently I also started using a voice recorder, dictating thoughts and ideas and doing story development and that sort of thing when I'm driving or hiking. I can get in the zone really easily that way, not having to use my hands for anything and not having a laptop with the lure of the internet one click away. Of course then I have to transcribe the ideas later, but I find it's valuable hearing my spoken ideas out loud.