The flight was British Airways from Detroit-Metro to London-Heathrow, the start of what would be several months of gallivanting around Europe with plenty of Ryanair seats and stuffy train compartments ahead. Paying $40 for a small pillow didn't seem all that bad, and what an excellent decision that impulse buy turned out to be.
That pillow (which squishes down to fit in a pouch a little larger than a fist and hooks onto my totebag strap) has saved my back on thin-cushioned seats, saved my butt when sitting for 10+ hours, saved my lumbar area even in the plushest business class seats, and been my only source of comfort on hard airport floors.
Currently it's missing, as I hid it from my cat (who mistook it for a play toy) and I've forgotten where I put it. Maybe it's time to buy another? Amazon still has them!
What was the best thing you ever bought in an airport? Share your story in comments below!