Magpul recently came out with a pair of handy field guide references for the long range shooter, the company's precision rifle data book 2.0 and quick reference cards. Both references are semi-rigid and can be written on using pencils, dry erase markers and other semi-permanent means (and can be cleaned with alcohol-based cleaners to be returned to like-new status). They're weather proof and can be carried together or separately.
The quick reference cards give pointers and reminders for both shooters and spotters. There are note cards available for jotting quick notes about a particular range trip, and also quick charts specific to certain elevations for keeping track of wind and range elements.
The precision rifle data book 2.0 contains cards for keeping notes, cards with information on altitude and density and cards for tracking all aspects of long-range shooting. Elevation-specific cards to help keep a record of all shots at ranges and environmental conditions are included.