An English-language letter frequency table I memorised in 6th(?) grade after reading Alvin’s Secret Code: ETAONRISHDLFCMUGYPWBVKXJQZ.
I know how to say 2183 in Italian.
For a 7th grade project I had to translate and then write out the Jabberwocky and The Raven in Norse Runes on distressed paper grocery bags.
Tends to stay with you decades later.
Also. LyNPgV7Z, my old dial up password that I did not pick, was case sensitive, and I could not change…
Tu si pazzo, you are crazy. That is all the Italian I know, and that bit is thanks to Catch-22.
Though now that I think about it, A Clockwork Orange taught me plenty of Russian.
I’m picturing you saying, “twenty one eighty three”, but waving a hand around whilst saying it.
Times tables, 9’s. In the third grade. I’d sing it on the walk home from school and still don’t skip a beat:
9, 18, 27, 36, 45, 54, 63, 72, 81, 90
Only up to 10x9.
bank account #, routing #, library card number
Arlington
Berkley
Clarendon
Dartmouth
Exeter
Fairfield
Gloucester
Hereford
Mass. Ave
The names of the first nine streets crossing Boston’s Back Bay, going west from the Boston Public Gardens
My drivers license number, because we used to write checks, and they always wanted the DL number, and I had my social on my checks at the time because I usually use AAFES where they didn’t want the DL, and we threw around SSAN’s like nothing back then.
Let’s see–like several others, I used to do community theater and singing in choruses (in public–that’s mad enough, I think). Though it’s been years since I last performed, I still recall the words and the tenor parts of many of these pieces. Not all. My memory for spoken lines is apparently not as good, though–fewer of them are rattling around my brain. However, quite a few poems are in there and won’t come out.
All the states, in alphabetical order, order of admission to the US, and order of physical area, though there is some dispute about the last list. All the state capitals, in alphabetical order. Most of the world capitals. An enormous number of facts relating to baseball, such as Joe Torre’s batting average in 1971 (.363) and Don Kessinger’s uniform number (11). A whole mess of other miscellaneous facts, most of which I have no earthly use for at this stage of my life.
Like @fedman, my routing number and checking account number, also my library card number. My social security number, along with my late wife’s, my son’s, and my daughter’s (but not yet my grandson’s). My best friend’s phone number from 1972. A surprising number of area codes. The north-south streets in my Chicago neighborhood growing up from east to west; I’d have to work out west to east, and the east-west streets north to south or south to north don’t count because they were basically all consecutive numbers.
I’m sure there’s more. But I can’t remember it 
Somebody mentioned the “Scarlet Pimpernel” recently, and much to my surprise, I came right out with:
"They seek him here, they seek him there,
Those Frenchies seek him everywhere.
Is he in heaven? Or is he in h***?
That demmed, elusive, Pimpernel!!"
Almost all of Handel’s Messiah.
Schubert’s Der Erlköaut;nig
Richard Cory (setting by Charles Naginski)
Unintentionally:
Jabberwocky.
The Owl and the Pussycat (via a 45rpm record I listened to many times as a child.)
When I was a kid, the only non-classical albums my parents had were the soundtracks of Carousel and The Sound Of Music. My sisters and I knew each and every word from each and every song on those albums. If asked, I probably could still sing them.
Please don’t ask.
The Greek alphabet, comes in handy sometimes for crossword puzzle solutions.
And, all the lyrics to Paul Simon’s “You Can Call Me Al”, which does not come in handy for crossword puzzle solutions.
The streets in my home town in New Jersey that run parallel to each other are in alphabetical order, too. But for some weird reason they’ve got two G’s
More inadvertent (whether I liked it or not)
Two all-beef patties special sauce lettuce cheese pickles onions on a sesame seed bun.
Every Good Boy Does Fine (If I’d grown up in Britain I guess I would have picked up Every Good Boy Deserves Favor).
Or perhaps, Favour?
I had no idea the UKers did that one differently from Americans. Or, differently to Americans. Whichever.
Add me to the “two all beef patties list”. Also, the correct spelling of bologna from the Oscar Mayer commercial.
If you had asked me to recite the preamble to the Constitution, I would have drawn a blank.
But, just now, I sang it, and got about 90 percent. Thanks, Schoolhouse Rock.