While method of notation is a personal thing, I am a definite devotee of notebooks. I have a Rite in the Rain notebook I keep in my 8x10 backpack, and another I keep with my 4x5 kit. In general, though, I just write down all pertinent information in a type of notebook I have developed a bit of an obsession with - Moleskine notebooks. Everything I could ask for in a notebook - the pocket in back is particularly nice. I ge mine from Dick Blick, but they're available elsewhere, too.