Very useful tools for navigation:

• a large straight edge (eg a yard stick) for drawing in magnetic north, UTM lines, lat/long lines, etc...
• several pens for taking notes, never take just one - it'll fail the night before the race, right after they handed out the maps
• several pencils (preferably mechanical) for making preliminary markings on your maps, until you've re-verified them before drawing them in permanent ink
• several permanent markers (eg "Sharpies"), in case the map is water proof, and regular pen won't write on it well
• several colors of highlighters - create a system - one color for primary navigation routes, another color for secondary navigation routes, possibly a third color for tertiary navigation routes, and yet another color for notes and markings
• several UTM grid readers with every imaginable map scale - chances are you'll end up with an odd map scale on some map of yours
• a digital distance measuring device - the analog ones are fixed scales - digital ones can handle *any* custom scale you can imagine
• extra batteries for the digital scale measuring device (!!)
• 3"x5" or 5"x7" cards for taking notes on, number them in order that you'll need them - possibly write a number on your map, that correlates to the note card number as well for easy identification