Multiplication table.... One day I'll get those 7s and 8s.

(I'm 40).

0118999881999119725... 3

If you're involved in any kind of protest, the phone number of a lawyer. Hell, generalize this. Make sure you memorize numbers of at least the first few of your emergency contacts. You never know when you will be separated from your phone.

White-orange, orange, white-green, blue, white-blue, green, white-brown, brown.

P Sherman 42 wallaby Way Sydney

First aid procedures.

Proper sequence of attaching jumper cables.

Your SSN

Basically any song on guitar that I like. I can sing the entire song back to front, but I can't for the life of me remember the chord sequences. And I've been playing for many years.

How to convert various units of measurement. (Including between imperial and metric.)

2.54 centimeters in an inch. Degrees Fahrenheit is nine fifths of degrees Celsius plus 32. Stuff like that.

The standardized NATO phonetic alphabet

...for when you need to read alpha numeric codes or clarify spellings.

Especially with, how, inexplicably, phone connections seem to have gotten more garbly in recent years.

This code was invented to be reasonably understood as much as possible in less-than-ideal communication conditions.

As time goes on, civilian life is full of situations where you'll need to read off serial numbers, codes, or even spelling your own name, to somebody seemingly connected to you from a million miles away via coconuts and twine.

So, learn it, and you never need to go "M as in...uh...'Mancy'?" ever again! Your IT department might thank you.

...and let's be honest, it sounds kinda cool. :)

Converting between hexadecimal and binary. It's not that hard and it would've been useful many times, but I still haven't memorised it

The dimensions of the doorways in my house.

The general knowledge of prefixes, suffixes and sentence structure of the language families/subgroups, in order to better grasp a basic understanding of a common language when I encounter it, and be more respective - for example knowing when to use -kun, Fraulein, señora, and courteous actions native to the locale

Your wife's birthday?

Articles of German Nouns

how to navigate whatever town or city you live in without GPS

how to division in your head. i always have to go the long way round.

Your state's mental hygiene/commitment laws and the Convention on the Rights of Persons with Disabilities treaty that U.S.A. is the only country not to ratify.

Fa Do Sol Ré La Mi Si
(F....C....G....D...A...E...B)

this is the order in which sharps go. Gives you the tonality of a given song. Let's say the song takes 4 sharps- take the last one (Ré/D), add a half-tone to it (Mi/E), there it is, your song is in E major

It works with flats as well, in the reverse order (Si Mi La Ré Sol Do Fa). Take the next-to-last flat, that is your tonality.

The first 100 digits of pi lol. On a more serious note, it is very useful to remember how you should react to certain comments you know others will make in the future.

Keeping it practical, I'd like to know the basics about every regionally important city in the world. Capitals should be easy, I probably have most of them down already, and I have a few ideas about how to compile a list of the rest.