I didn't find it while riding, but it's come in handy quite a few times on the bike.
A long time ago, before I even had a drivers license, I was up at our weekend cabin walking back from the lake along the gravel road. I found a sleeping bag in a stuff sack.
It's been more than 20 years and I still have it, and as it's down, it's probably the best bag I have in my camping gear. Packs up tiny and is the warmest bag I own. I'd like to replace it, but similar models today are at least ~$200. That bag has been with me all over the country on my bike.