Probably a couple million sats for a conference/event ticket, but to be honest every purchase has Bitcoin as its opportunity cost so technically the deposit I paid for my home in 2020 could have stacked sats.
My biggest single Bitcoin purchase was a New Roof, siding, driveway, and new concrete front walkway. Wasn't the best time to sell to accomplish those things, but they needed done and I'm glad I had the Bitcoin to do it.
I let my fiat sit in bitcoin and then exchange it for cash and use that to pay rent. My rent has gotten cheaper when priced in sats which is very cool.
I've bought so many things and can't exactly remember which one is the most expensive. I even bought a diamond ring, but then I bought a bike either of the two. Sats wise the ring was more expensive, price wise in shit the cycle.