This reminds me of the time I sold a ca. $300 wool and silk suit to a US buyer, had it all packaged up to go by Xpresspost, and just as my husband was starting the car, I realized I'd forgotten to include the satin belt, without which the jacket would be virtually useless (it was button-less and needed the belt to provide a closure). Stopped said husband, tore open said box, murmured a "thank you" to the powers that be, and off it went again.
It was good of you to be so kind to your postal people -- what a nice gesture. People really appreciate spontaneous acts of thoughtfulness, especially if they aren't anticipated (those are the very best kind!).
Speaking of boxes, the other day I had to "fabricate" essentially a gigantic pizza box shape out of an old large Home Depot box in order to ship a hat that was 21" across the brim. It was a rather hilarious job and took me over an hour. Stuffed it with paper and air-bags, plastered it with "Do Not Crush" stickers and the whole thing barely weighed 800gm. Still, at 22" x 20" x 6", it was unfortunately beyond the pale for Expedited and cost me dearly to send. I'm keeping my fingers crossed that the buyer gets the hat "un-squished". It's probably the last time I'll try selling something that size and shape.