Is there anything you have found worth memorizing for instant recall?

Mnemonic major system helps you remember other things if you memorise it:

https://en.wikipedia.org/wiki/Mnemonic_major_system

Simple past and past participle of irregular english verbs.

Several phone numbers I want to know in case I don't have my phone and want to call one or more of them. Names of people I just met. Recipes I make often enough and don't want to bother getting out the binder/book/tablet for. Keyboard shortcuts, like for copy and paste and also for boot options on Dell, HP, etc. My social security number and those of my immediate family members. Birthdays.

Things like this.

Sure; knowing the powers of 2 up to 2^32, and the first 20 digits of both pi and e, are great for providing geek cred.

NATO phonetic alphabet.