Here’s an interesting topic on Ask MetaFilter:

I have a graph-ruled Moleskine that is begging to be turned into a compendium of obscure, fascinating, and perhaps occasionally useful reference material. Some of the things I want to put in there are Rubik’s Cube algorithms, keys to reading non-Latin alphabets, some simple math formulas (Trachtenberg math, e.g.), rules of thumb for estimating distance/altitude, and whatever else. I’m imagining the user would bust it out of his/her bag and use the knowledge within to solve a wide range of MacGyver/James Bond/bar bet problems. An intellectual “Swiss army knife”, if you will. Any and all ideas are welcome!

There are a wide variety of responses:

Pi to a thousand places
Resistor color codes
PID loop tuning hints and tricks
BIOS entry keys for a large number of brands of computers
Nomographs for: F to C and temp/humidity to dew point
Look up tables for Sine, Cosine and Tangent
Common Op-amp designs like inverting, integrating, etc
Common transistor designs like Common Emitter, Common collector, etc
Integral and Derivative tables
Trig Identities
Since others are pointing out that pocket compendia exist already, perhaps you could tailor the Moleskine to have knowledge specific to you. How about a scale diagram of your home, so that if you’re buying furniture/planning repairs/etc. you will have the right dimensions handy?
Time zones
zip and area codes
square root by hand
most common famous quotes
doing math with Roman numerals
commonly misspelled words
some words that start with each letter of the alphabet
Hebrew vowels
Historical periods
top 100 books/films
Instructions for identifying, cultivating, and refining penicillin.
standard factory admin passwords to routers and bios, etc.
adhere a super thin mirror (maybe mylar) to one of the inside covers
phone numbers to global car rental, travel agencies, hotels and concierge services
Dance steps
The catalogue of Messier objects
In addition to edible plants, I’d include section with details and sketches of local poisonous/toxic plants, with info on how to immediately deal with exposure.
On the practical side you should put down your medical history and any prescriptions you’re taking. If you get sent to the hospital it would be very helpful not to have to remember all the names of the meds you’re taking. Especially if you’re bleeding profusely or just had a blow to the head. If you wear glasses or contacts, put that prescription in too.
Draw some game boards across double page spreads, and keep paper playing pieces in the back pouch. My travel notebook now has boards and pieces for chess or draughts, backgammon and go. These pages get much more use (on flights, etc) than the foreign phrases, unit conversion tables (weight, volume, temperature, distance), time zone lookups, etc that I wrote in there.
How about a sundial with notes on its use? You just need the dial, use a pen, matchstick or finger as a gnomon. Only useful if you know where north is, of course.

And so many more… I love the variety, from techno-geekery to first aid, to arts and literature to sports to astronomy to clothing sizes and on and on…
I love this idea because each person’s list will be different– so many diaries come with time zones and conversion charts and national holidays, but undated notebooks almost never do… and wouldn’t you rather have lists of the specific things that are important to you? And what does it tell you about a person to know what sorts of information they think they’d need in an emergency?

Here are some bits of information that I’ve carried around in notebooks at various times:

• Maps of NYC subways and buses
• Maps of Central Park and Prospect Park
• World map
• My measurements and clothing sizes
• Phone numbers and birthdays of family and close friends
• Conversion charts
• A cheat sheet of information (dates, sales figures, etc) pertaining to my job
• Passwords
• Lists of Pulitzer Prize and Booker Prize-winning books
• Phone numbers of local restaurants
• The sign language alphabet
• A band-aid

What information would you keep in your mental swiss-army notebook?

Read more at Mental Swiss-Army Knife (in a Moleskine) | Ask MetaFilter.